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All trademarks and registered trademarks are the property of their respective owners Contents About ................................................................................................................................................................................... 1 Chapter 1: Getting started with Oracle Database ....................................................................................... 2 Section 1.1: Hello World ................................................................................................................................................. 2 Section 1.2: SQL Query .................................................................................................................................................. 2 Section 1.3: Hello world! from table .............................................................................................................................. 2 Section 1.4: Hello World from PL/SQL ......................................................................................................................... 3 Chapter 2: Getting started with PL/SQL ........................................................................................................... 4 Section 2.1: Hello World ................................................................................................................................................. 4 Section 2.2: Definition of PL/SQL ................................................................................................................................. 4 Section 2.3: Dierence between %TYPE and %ROWTYPE ........................................................................................ 5 Section 2.4: Create or replace a view .......................................................................................................................... 6 Section 2.5: Create a table ........................................................................................................................................... 6 Section 2.6: About PL/SQL ........................................................................................................................................... 6 Chapter 3: Anonymous PL/SQL Block ................................................................................................................ 8 Section 3.1: An example of an anonymous block ....................................................................................................... 8 Chapter 4: PL/SQL procedure ............................................................................................................................... 9 Section 4.1: Syntax ......................................................................................................................................................... 9 Section 4.2: Hello World ................................................................................................................................................ 9 Section 4.3: In/Out Parameters ................................................................................................................................... 9 Chapter 5: Data Dictionary ................................................................................................................................... 11 Section 5.1: Describes all objects in the database ................................................................................................... 11 Section 5.2: To see all the data dictionary views to which you have access ........................................................ 11 Section 5.3: Text source of the stored objects ......................................................................................................... 11 Section 5.4: Get list of all tables in Oracle ................................................................................................................. 11 Section 5.5: Privilege information .............................................................................................................................. 11 Section 5.6: Oracle version ......................................................................................................................................... 12 Chapter 6: Dates ......................................................................................................................................................... 13 Section 6.1: Date Arithmetic - Dierence between Dates in Days, Hours, Minutes and/or Seconds ................. 13 Section 6.2: Setting the Default Date Format Model ............................................................................................... 14 Section 6.3: Date Arithmetic - Dierence between Dates in Months or Years ...................................................... 14 Section 6.4: Extract the Year, Month, Day, Hour, Minute or Second Components of a Date .............................. 15 Section 6.5: Generating Dates with No Time Component ....................................................................................... 16 Section 6.6: Generating Dates with a Time Component ......................................................................................... 16 Section 6.7: The Format of a Date ............................................................................................................................. 17 Section 6.8: Converting Dates to a String ................................................................................................................. 17 Section 6.9: Changing How SQL/Plus or SQL Developer Display Dates ............................................................... 18 Section 6.10: Time Zones and Daylight Savings Time ............................................................................................. 18 Section 6.11: Leap Seconds ......................................................................................................................................... 19 Section 6.12: Getting the Day of the Week ............................................................................................................... 19 Chapter 7: Working with Dates ........................................................................................................................... 20 Section 7.1: Date Arithmetic ........................................................................................................................................ 20 Section 7.2: Add_months function ............................................................................................................................ 20 Chapter 8: DUAL table ............................................................................................................................................. 22 Section 8.1: The following example returns the current operating system date and time .................................. 22 Section 8.2: The following example generates numbers between start_value and end_value ........................ 22 Chapter 9: JOINS ......................................................................................................................................................... 23 Section 9.1: CROSS JOIN ............................................................................................................................................. 23 Section 9.2: LEFT OUTER JOIN .................................................................................................................................. 24 Section 9.3: RIGHT OUTER JOIN ................................................................................................................................ 25 Section 9.4: FULL OUTER JOIN .................................................................................................................................. 27 Section 9.5: ANTIJOIN ................................................................................................................................................. 28 Section 9.6: INNER JOIN ............................................................................................................................................. 29 Section 9.7: JOIN ......................................................................................................................................................... 30 Section 9.8: SEMIJOIN ................................................................................................................................................. 30 Section 9.9: NATURAL JOIN ....................................................................................................................................... 31 Chapter 10: Handling NULL values .................................................................................................................... 33 Section 10.1: Operations containing NULL are NULL, except concatenation ........................................................ 33 Section 10.2: NVL2 to get a dierent result if a value is null or not ....................................................................... 33 Section 10.3: COALESCE to return the first non-NULL value ................................................................................... 33 Section 10.4: Columns of any data type can contain NULLs .................................................................................. 33 Section 10.5: Empty strings are NULL ....................................................................................................................... 33 Section 10.6: NVL to replace null value ..................................................................................................................... 34 Chapter 11: String Manipulation ........................................................................................................................... 35 Section 11.1: INITCAP .................................................................................................................................................... 35 Section 11.2: Regular expression ................................................................................................................................ 35 Section 11.3: SUBSTR ................................................................................................................................................... 35 Section 11.4: Concatenation: Operator || or concat() function ................................................................................ 36 Section 11.5: UPPER ...................................................................................................................................................... 36 Section 11.6: LOWER .................................................................................................................................................... 37 Section 11.7: LTRIM / RTRIM ....................................................................................................................................... 37 Chapter 12: IF-THEN-ELSE Statement .............................................................................................................. 38 Section 12.1: IF-THEN ................................................................................................................................................... 38 Section 12.2: IF-THEN-ELSE ........................................................................................................................................ 38 Section 12.3: IF-THEN-ELSIF-ELSE .............................................................................................................................. 38 Chapter 13: Limiting the rows returned by a query (Pagination) ...................................................... 39 Section 13.1: Get first N rows with row limiting clause .............................................................................................. 39 Section 13.2: Get row N through M from many rows (before Oracle 12c) ............................................................. 39 Section 13.3: Get N numbers of Records from table ................................................................................................ 39 Section 13.4: Skipping some rows then taking some ............................................................................................... 40 Section 13.5: Skipping some rows from result .......................................................................................................... 40 Section 13.6: Pagination in SQL .................................................................................................................................. 40 Chapter 14: Recursive Sub-Query Factoring using the WITH Clause (A.K.A. Common Table Expressions) ..................................................................................................................................................... 42 Section 14.1: Splitting a Delimited String .................................................................................................................... 42 Section 14.2: A Simple Integer Generator .................................................................................................................. 42 Chapter 15: Dierent ways to update records ........................................................................................... 44 Section 15.1: Update using Merge .............................................................................................................................. 44 Section 15.2: Update Syntax with example ............................................................................................................... 44 Section 15.3: Update Using Inline View ...................................................................................................................... 44 Section 15.4: Merge with sample data ....................................................................................................................... 45 Chapter 16: Update with Joins ............................................................................................................................. 47 Section 16.1: Examples: what works and what doesn't ............................................................................................. 47 Chapter 17: Functions ............................................................................................................................................... 49 Section 17.1: Calling Functions .................................................................................................................................... 49 Chapter 18: Statistical functions ......................................................................................................................... 50 Section 18.1: Calculating the median of a set of values ........................................................................................... 50 Chapter 19: Window Functions ............................................................................................................................. 51 Section 19.1: Ratio_To_Report ................................................................................................................................... 51 Chapter 20: Creating a Context .......................................................................................................................... 52 Section 20.1: Create a Context ................................................................................................................................... 52 Chapter 21: Splitting Delimited Strings ............................................................................................................ 53 Section 21.1: Splitting Strings using a Hierarchical Query ........................................................................................ 53 Section 21.2: Splitting Strings using a PL/SQL Function .......................................................................................... 53 Section 21.3: Splitting Strings using a Recursive Sub-query Factoring Clause ..................................................... 54 Section 21.4: Splitting Strings using a Correlated Table Expression ...................................................................... 55 Section 21.5: Splitting Strings using CROSS APPLY (Oracle 12c) ............................................................................. 56 Section 21.6: Splitting Strings using XMLTable and FLWOR expressions .............................................................. 57 Section 21.7: Splitting Delimited Strings using XMLTable ........................................................................................ 57 Chapter 22: Collections and Records ............................................................................................................... 59 Section 22.1: Use a collection as a return type for a split function ........................................................................ 59 Chapter 23: Object Types ....................................................................................................................................... 60 Section 23.1: Accessing stored objects ...................................................................................................................... 60 Section 23.2: BASE_TYPE ........................................................................................................................................... 60 Section 23.3: MID_TYPE .............................................................................................................................................. 61 Section 23.4: LEAF_TYPE ............................................................................................................................................ 62 Chapter 24: Loop ........................................................................................................................................................ 64 Section 24.1: Simple Loop ........................................................................................................................................... 64 Section 24.2: WHILE Loop ........................................................................................................................................... 64 Section 24.3: FOR Loop ............................................................................................................................................... 64 Chapter 25: Cursors ................................................................................................................................................... 67 Section 25.1: Parameterized "FOR loop" Cursor ...................................................................................................... 67 Section 25.2: Implicit "FOR loop" cursor ................................................................................................................... 67 Section 25.3: Handling a CURSOR ............................................................................................................................. 67 Section 25.4: Working with SYS_REFCURSOR ......................................................................................................... 68 Chapter 26: Sequences ............................................................................................................................................ 69 Section 26.1: Creating a Sequence: Example ............................................................................................................ 69 Chapter 27: Indexes ................................................................................................................................................... 71 Section 27.1: b-tree index ............................................................................................................................................ 71 Section 27.2: Bitmap Index ......................................................................................................................................... 71 Section 27.3: Function Based Index ........................................................................................................................... 71 Chapter 28: Hints ........................................................................................................................................................ 72 Section 28.1: USE_NL .................................................................................................................................................. 72 Section 28.2: APPEND HINT ........................................................................................................................................ 72 Section 28.3: Parallel Hint ........................................................................................................................................... 72 Section 28.4: USE_HASH ............................................................................................................................................ 73 Section 28.5: FULL ....................................................................................................................................................... 73 Section 28.6: Result Cache ......................................................................................................................................... 74 Chapter 29: Packages ............................................................................................................................................... 75 Section 29.1: Define a Package header and body with a function ......................................................................... 75 Section 29.2: Overloading .......................................................................................................................................... 75 Section 29.3: Package Usage ..................................................................................................................................... 76 Chapter 30: Exception Handling .......................................................................................................................... 78 Section 30.1: Syntax ..................................................................................................................................................... 78 Section 30.2: User defined exceptions ...................................................................................................................... 78 Section 30.3: Internally defined exceptions .............................................................................................................. 79 Section 30.4: Predefined exceptions .......................................................................................................................... 80 Section 30.5: Define custom exception, raise it and see where it comes from ..................................................... 81 Section 30.6: Handling connexion error exceptions ................................................................................................ 82 Section 30.7: Exception handling ............................................................................................................................... 83 Chapter 31: Error logging ........................................................................................................................................ 84 Section 31.1: Error logging when writing to database .............................................................................................. 84 Chapter 32: Database Links .................................................................................................................................. 85 Section 32.1: Creating a database link ...................................................................................................................... 85 Section 32.2: Create Database Link .......................................................................................................................... 85 Chapter 33: Table partitioning ............................................................................................................................. 87 Section 33.1: Select existing partitions ....................................................................................................................... 87 Section 33.2: Drop partition ........................................................................................................................................ 87 Section 33.3: Select data from a partition ................................................................................................................ 87 Section 33.4: Split Partition ......................................................................................................................................... 87 Section 33.5: Merge Partitions .................................................................................................................................... 87 Section 33.6: Exchange a partition ............................................................................................................................ 87 Section 33.7: Hash partitioning .................................................................................................................................. 88 Section 33.8: Range partitioning ................................................................................................................................ 88 Section 33.9: List partitioning ..................................................................................................................................... 88 Section 33.10: Truncate a partition ............................................................................................................................ 89 Section 33.11: Rename a partition .............................................................................................................................. 89 Section 33.12: Move partition to dierent tablespace ............................................................................................. 89 Section 33.13: Add new partition ................................................................................................................................ 89 Chapter 34: Oracle Advanced Queuing (AQ) ................................................................................................ 90 Section 34.1: Simple Producer/Consumer ................................................................................................................. 90 Chapter 35: constraints ........................................................................................................................................... 94 Section 35.1: Update foreign keys with new value in Oracle .................................................................................. 94 Section 35.2: Disable all related foreign keys in oracle .......................................................................................... 94 Chapter 36: Autonomous Transactions ........................................................................................................... 95 Section 36.1: Using autonomous transaction for logging errors ............................................................................ 95 Chapter 37: Oracle MAF ........................................................................................................................................... 96 Section 37.1: To get value from Binding .................................................................................................................... 96 Section 37.2: To set value to binding ......................................................................................................................... 96 Section 37.3: To invoke a method from binding ...................................................................................................... 96 Section 37.4: To call a javaScript function ................................................................................................................ 96 Chapter 38: level query ........................................................................................................................................... 97 Section 38.1: Generate N Number of records ........................................................................................................... 97 Section 38.2: Few usages of Level Query ................................................................................................................. 97 Chapter 39: Hierarchical Retrieval With Oracle Database 12C ........................................................... 98 Section 39.1: Using the CONNECT BY Caluse ............................................................................................................ 98 Section 39.2: Specifying the Direction of the Query From the Top Down ............................................................ 98 Chapter 40: Data Pump .......................................................................................................................................... 99 Section 40.1: Monitor Datapump jobs ....................................................................................................................... 99 Section 40.2: Step 3/6 : Create directory .................................................................................................................. 99 Section 40.3: Step 7 : Export Commands .................................................................................................................. 99 Section 40.4: Step 9 : Import Commands ............................................................................................................... 100 Section 40.5: Datapump steps ................................................................................................................................. 101 Section 40.6: Copy tables between dierent schemas and tablespaces ........................................................... 101 Chapter 41: Bulk collect ........................................................................................................................................ 102 Section 41.1: Bulk data Processing ........................................................................................................................... 102 Chapter 42: Real Application Security .......................................................................................................... 103 Section 42.1: Application ........................................................................................................................................... 103 Chapter 43: Assignments model and language ....................................................................................... 105 Section 43.1: Assignments model in PL/SQL .......................................................................................................... 105 Chapter 44: Triggers .............................................................................................................................................. 107 Section 44.1: Before INSERT or UPDATE trigger .................................................................................................... 107 Chapter 45: Dynamic SQL .................................................................................................................................... 108 Section 45.1: Select value with dynamic SQL .......................................................................................................... 108 Section 45.2: Insert values in dynamic SQL ............................................................................................................ 108 Section 45.3: Update values in dynamic SQL ......................................................................................................... 108 Section 45.4: Execute DDL statement ..................................................................................................................... 109 Section 45.5: Execute anonymous block ................................................................................................................ 109 Credits ............................................................................................................................................................................ 110 You may also like ...................................................................................................................................................... 112 About Please feel free to share this PDF with anyone for free, latest version of this book can be downloaded from: https://goalkicker.com/OracleDatabaseBook This Oracle® Database Notes for Professionals book is compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA, see credits at the end of this book whom contributed to the various chapters. Images may be copyright of their respective owners unless otherwise specified This is an unofficial free book created for educational purposes and is not affiliated with official Oracle® Database group(s) or company(s) nor Stack Overflow. All trademarks and registered trademarks are the property of their respective company owners The information presented in this book is not guaranteed to be correct nor accurate, use at your own risk Please send feedback and corrections to web@petercv.com GoalKicker.com – Oracle® Database Notes for Professionals 1 Chapter 1: Getting started with Oracle Database Version Release Date Version 1 (unreleased) 1978-01-01 Oracle V2 1979-01-01 Oracle Version 3 1983-01-01 Oracle Version 4 1984-01-01 Oracle Version 5 1985-01-01 Oracle Version 6 1988-01-01 Oracle7 1992-01-01 Oracle8 1997-07-01 Oracle8i 1999-02-01 Oracle9i 2001-06-01 Oracle 10g 2003-01-01 Oracle 11g 2007-01-01 Oracle 12c 2013-01-01 Section 1.1: Hello World SELECT 'Hello world!' FROM dual; In Oracle's flavor of SQL, "dual is just a convienence table". It was originally intended to double rows via a JOIN, but now contains one row with a DUMMY value of 'X'. Section 1.2: SQL Query List employees earning more than $50000 born this century. List their name, date of birth and salary, sorted alphabetically by name. SELECT employee_name, date_of_birth, salary FROM employees WHERE salary > 50000 AND date_of_birth >= DATE '2000-01-01' ORDER BY employee_name; Show the number of employees in each department with at least 5 employees. List the largest departments first. SELECT department_id, COUNT(*) FROM employees GROUP BY department_id HAVING COUNT(*) >= 5 ORDER BY COUNT(*) DESC; Section 1.3: Hello world! from table Create a simple table CREATE TABLE MY_table ( what VARCHAR2(10), who VARCHAR2(10), GoalKicker.com – Oracle® Database Notes for Professionals 2 mark VARCHAR2(10) ); Insert values (you can omit target columns if you provide values for all columns) INSERT INTO my_table (what, who, mark) VALUES ('Hello', 'world', '!' ); INSERT INTO my_table VALUES ('Bye bye', 'ponies', '?' ); INSERT INTO my_table (what) VALUES('Hey'); Remember to commit, because Oracle uses transactions COMMIT; Select your data: SELECT what, who, mark FROM my_table WHERE what='Hello'; Section 1.4: Hello World from PL/SQL /* PL/SQL is a core Oracle Database technology, allowing you to build clean, secure, optimized APIs to SQL and business logic. */ SET serveroutput ON BEGIN DBMS_OUTPUT.PUT_LINE ('Hello World!'); END; GoalKicker.com – Oracle® Database Notes for Professionals 3 Chapter 2: Getting started with PL/SQL Section 2.1: Hello World SET serveroutput ON DECLARE message CONSTANT VARCHAR2(32767):= 'Hello, World!'; BEGIN DBMS_OUTPUT.put_line(message); END; / Command SET serveroutput ON is required in SQL*Plus and SQL Developer clients to enable the output of DBMS_OUTPUT. Without the command nothing is displayed. The END; line signals the end of the anonymous PL/SQL block. To run the code from SQL command line, you may need to type / at the beginning of the first blank line after the last line of the code. When the above code is executed at SQL prompt, it produces the following result: Hello, World! PL/SQL procedure successfully completed. Section 2.2: Definition of PL/SQL PL/SQL (Procedural Language/Structured Query Language) is Oracle Corporation's procedural extension for SQL and the Oracle relational database. PL/SQL is available in Oracle Database (since version 7), TimesTen in-memory database (since version 11.2.1), and IBM DB2 (since version 9.7). The basic unit in PL/SQL is called a block, which is made up of three parts: a declarative part, an executable part, and an exception-building part. DECLARE BEGIN EXCEPTION END; Declarations - This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program. Executable Commands - This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable line of code, which may be just a NULL command to indicate that nothing should be executed. Exception Handling - This section starts with the keyword EXCEPTION. This section is again optional and contains exception(s) that handle errors in the program. Every PL/SQL statement ends with a semicolon (;). PL/SQL blocks can be nested within other PL/SQL blocks using BEGIN and END. GoalKicker.com – Oracle® Database Notes for Professionals 4 In anonymous block, only executable part of block is required, other parts are not nessesary. Below is example of simple anonymous code, which does not do anything but perform without error reporting. BEGIN NULL; END; / Missing excecutable instruction leads to an error, becouse PL/SQL does not support empty blocks. For example, excecution of code below leads to an error: BEGIN END; / Application will raise error: END; * ERROR AT line 2: ORA-06550: line 2, column 1: PLS-00103: Encountered the symbol "END" WHEN expecting one OF the following: ( BEGIN CASE DECLARE EXIT FOR GOTO IF LOOP MOD NULL PRAGMA RAISE RETURN SELECT UPDATE WHILE WITH << continue CLOSE CURRENT DELETE FETCH LOCK INSERT OPEN ROLLBACK SAVEPOINT SET SQL EXECUTE COMMIT FORALL MERGE pipe purge Symbol " * " in line below keyword "END;" means, that the block which ends with this block is empty or bad constructed. Every execution block needs instructions to do, even if it does nothing, like in our example. Section 2.3: Dierence between %TYPE and %ROWTYPE %TYPE: Used to declare a field with the same type as that of a specified table's column. DECLARE vEmployeeName Employee.Name%TYPE; BEGIN SELECT Name INTO vEmployeeName FROM Employee WHERE ROWNUM = 1; DBMS_OUTPUT.PUT_LINE(vEmployeeName); END; / %ROWTYPE: Used to declare a record with the same types as found in the specified table, view or cursor (= multiple columns). DECLARE rEmployee Employee%ROWTYPE; BEGIN rEmployee.Name := 'Matt'; rEmployee.Age := 31; DBMS_OUTPUT.PUT_LINE(rEmployee.Name); GoalKicker.com – Oracle® Database Notes for Professionals 5 DBMS_OUTPUT.PUT_LINE(rEmployee.Age); END; / Section 2.4: Create or replace a view In this example we are going to create a view. A view is mostly used as a simple way of fetching data from multiple tables. Example 1: View with a select on one table. CREATE OR REPLACE VIEW LessonView AS SELECT L.* FROM Lesson L; Example 2: View with a select on multiple tables. CREATE OR REPLACE VIEW ClassRoomLessonView AS SELECT C.Id, C.Name, L.Subject, L.Teacher FROM ClassRoom C, Lesson L WHERE C.Id = L.ClassRoomId; To call this views in a query you can use a select statement. SELECT * FROM LessonView; SELECT * FROM ClassRoomLessonView; Section 2.5: Create a table Below we are going to create a table with 3 columns. The column Id must be filled is, so we define it NOT NULL. On the column Contract we also add a check so that the only value allowed is 'Y' or 'N'. If an insert in done and this column is not specified during the insert then default a 'N' is inserted. CREATE TABLE Employee ( Id NUMBER NOT NULL, Name VARCHAR2(60), Contract CHAR DEFAULT 'N' NOT NULL, --- CONSTRAINT p_Id PRIMARY KEY(Id), CONSTRAINT c_Contract CHECK (Contract IN('Y','N')) ); Section 2.6: About PL/SQL PL/SQL stands for Procedural Language extensions to SQL. PL/SQL is available only as an "enabling technology" within other software products; it does not exist as a standalone language. You can use PL/SQL in the Oracle relational database, in the Oracle Server, and in client-side application development tools, such as Oracle Forms. Here are some of the ways you might use PL/SQL: GoalKicker.com – Oracle® Database Notes for Professionals 6 1. To build stored procedures. . 2. To create database triggers. 3. To implement client-side logic in your Oracle Forms application. 4. To link a World Wide Web home page to an Oracle database. GoalKicker.com – Oracle® Database Notes for Professionals 7 Chapter 3: Anonymous PL/SQL Block Section 3.1: An example of an anonymous block DECLARE -- declare a variable message VARCHAR2(20); BEGIN -- assign value to variable message := 'HELLO WORLD'; -- print message to screen DBMS_OUTPUT.PUT_LINE(message); END; / GoalKicker.com – Oracle® Database Notes for Professionals 8 Chapter 4: PL/SQL procedure PL/SQL procedure is a group of SQL statements stored on the server for reuse. It increases the performance because the SQL statements do not have to be recompiled every time it is executed. Stored procedures are useful when same code is required by multiple applications. Having stored procedures eliminates redundancy, and introduces simplicity to the code. When data transfer is required between the client and server, procedures can reduce communication cost in certain situations. Section 4.1: Syntax CREATE [OR REPLACE] PROCEDURE procedure_name [(parameter_name [IN | OUT | IN OUT] TYPE [, ...])] {IS | AS} < declarations > BEGIN < procedure_body > EXCEPTION -- Exception-handling part begins WHEN exception1 THEN exception1-handling-statements END procedure_name; procedure-name specifies the name of the procedure. [OR REPLACE] option allows modifying an existing procedure. The optional parameter list contains name, mode and types of the parameters. IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure. If no mode is specified, parameter is assumed to be of IN mode. In the declaration section we can declare variables which will be used in the body part. procedure-body contains the executable part. The AS keyword is used instead of the IS keyword for creating a standalone procedure. exception section will handle the exceptions from the procedure. This section is optional. Section 4.2: Hello World The following simple procedure displays the text "Hello World" in a client that supports DBMS_OUTPUT. CREATE OR REPLACE PROCEDURE helloworld AS BEGIN DBMS_OUTPUT.put_line('Hello World!'); END; / You need to execute this at the SQL prompt to create the procedure in the database, or you can run the query below to get the same result: SELECT 'Hello World!' FROM dual; Section 4.3: In/Out Parameters PL/SQL uses IN, OUT, IN OUT keywords to define what can happen to a passed parameter. IN specifies that the parameter is read only and the value cannot be changed by the procedure. GoalKicker.com – Oracle® Database Notes for Professionals 9 OUT specifies the parameter is write only and a procedure can assign a value to it, but not reference the value. IN OUT specifies the parameter is available for reference and modification. PROCEDURE procedureName(x IN INT, strVar IN VARCHAR2, ans OUT VARCHAR2) ... ... END procedureName; procedureName(firstvar, secondvar, thirdvar); The variables passed in the above example need to be typed as they are defined in the procedure parameter section. GoalKicker.com – Oracle® Database Notes for Professionals 10 Chapter 5: Data Dictionary Section 5.1: Describes all objects in the database SELECT * FROM dba_objects Section 5.2: To see all the data dictionary views to which you have access SELECT * FROM dict Section 5.3: Text source of the stored objects USER_SOURCE describes the text source of the stored objects owned by the current user. This view does not display the OWNER column. SELECT * FROM user_source WHERE TYPE='TRIGGER' AND LOWER(text) LIKE '%order%' ALL_SOURCE describes the text source of the stored objects accessible to the current user. SELECT * FROM all_source WHERE owner=:owner DBA_SOURCE describes the text source of all stored objects in the database. SELECT * FROM dba_source Section 5.4: Get list of all tables in Oracle SELECT owner, table_name FROM all_tables ALL_TAB_COLUMNS describes the columns of the tables, views, and clusters accessible to the current user. COLS is a synonym for USER_TAB_COLUMNS. SELECT * FROM all_tab_columns WHERE table_name = :tname Section 5.5: Privilege information All roles granted to user. SELECT * FROM dba_role_privs WHERE grantee= :username Privileges granted to user: 1. system privileges SELECT * GoalKicker.com – Oracle® Database Notes for Professionals 11 FROM dba_sys_privs WHERE grantee = :username 2. object grants SELECT * FROM dba_tab_privs WHERE grantee = :username Permissions granted to roles. Roles granted to other roles. SELECT * FROM role_role_privs WHERE role IN (SELECT granted_role FROM dba_role_privs WHERE grantee= :username) 1. system privileges SELECT * FROM role_sys_privs WHERE role IN (SELECT granted_role FROM dba_role_privs WHERE grantee= :username) 2. object grants SELECT * FROM role_tab_privs WHERE role IN (SELECT granted_role FROM dba_role_privs WHERE grantee= :username) Section 5.6: Oracle version SELECT * FROM v$version GoalKicker.com – Oracle® Database Notes for Professionals 12 Chapter 6: Dates Section 6.1: Date Arithmetic - Dierence between Dates in Days, Hours, Minutes and/or Seconds In oracle, the difference (in days and/or fractions thereof) between two DATEs can be found using subtraction: SELECT DATE '2016-03-23' - DATE '2015-12-25' AS difference FROM DUAL; Outputs the number of days between the two dates: DIFFERENCE ---------- 89 And: SELECT TO_DATE( '2016-01-02 01:01:12', 'YYYY-MM-DD HH24:MI:SS' ) - TO_DATE( '2016-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS' ) AS difference FROM DUAL Outputs the fraction of days between two dates: DIFFERENCE ---------- 1.0425 The difference in hours, minutes or seconds can be found by multiplying this number by 24, 24*60 or 24*60*60 respectively. The previous example can be changed to get the days, hours, minutes and seconds between two dates using: SELECT TRUNC( difference ) AS days, TRUNC( MOD( difference * 24, 24 ) ) AS hours, TRUNC( MOD( difference * 24*60, 60 ) ) AS minutes, TRUNC( MOD( difference * 24*60*60, 60 ) ) AS seconds FROM ( SELECT TO_DATE( '2016-01-02 01:01:12', 'YYYY-MM-DD HH24:MI:SS' ) - TO_DATE( '2016-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS' ) AS difference FROM DUAL ); (Note: TRUNC() is used rather than FLOOR() to correctly handle negative differences.) Outputs: DAYS HOURS MINUTES SECONDS ---- ----- ------- ------- 1 1 1 12 GoalKicker.com – Oracle® Database Notes for Professionals 13 The previous example can also be solved by converting the numeric difference to an interval using NUMTODSINTERVAL(): SELECT EXTRACT( DAY FROM difference ) AS days, EXTRACT( HOUR FROM difference ) AS hours, EXTRACT( MINUTE FROM difference ) AS minutes, EXTRACT( SECOND FROM difference ) AS seconds FROM ( SELECT NUMTODSINTERVAL( TO_DATE( '2016-01-02 01:01:12', 'YYYY-MM-DD HH24:MI:SS' ) - TO_DATE( '2016-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS' ), 'DAY' ) AS difference FROM DUAL ); Section 6.2: Setting the Default Date Format Model When Oracle implicitly converts from a DATE to a string or vice-versa (or when TO_CHAR() or TO_DATE() are explicitly called without a format model) the NLS_DATE_FORMAT session parameter will be used as the format model in the conversion. If the literal does not match the format model then an exception will be raised. You can review this parameter using: SELECT VALUE FROM NLS_SESSION_PARAMETERS WHERE PARAMETER = 'NLS_DATE_FORMAT'; You can set this value within your current session using: ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS'; (Note: this does not change the value for any other users.) If you rely on the NLS_DATE_FORMAT to provide the format mask in TO_DATE() or TO_CHAR() then you should not be surprised when your queries break if this value is ever changed. Section 6.3: Date Arithmetic - Dierence between Dates in Months or Years The difference in months between two dates can be found using the MONTHS_BETWEEN( date1, date2 ): SELECT MONTHS_BETWEEN( DATE '2016-03-10', DATE '2015-03-10' ) AS difference FROM DUAL; Outputs: DIFFERENCE ---------- 12 If the difference includes part months then it will return the fraction of the month based on there being 31 days in each month: SELECT MONTHS_BETWEEN( DATE '2015-02-15', DATE '2015-01-01' ) AS difference FROM DUAL; Outputs: GoalKicker.com – Oracle® Database Notes for Professionals 14 DIFFERENCE ---------- 1.4516129 Due to MONTHS_BETWEEN assuming 31 days per month when there can be fewer days per month then this can result in different values for differences spanning the boundaries between months. Example: SELECT MONTHS_BETWEEN( DATE'2016-02-01', DATE'2016-02-01' - INTERVAL '1' DAY ) AS "JAN-FEB", MONTHS_BETWEEN( DATE'2016-03-01', DATE'2016-03-01' - INTERVAL '1' DAY ) AS "FEB-MAR", MONTHS_BETWEEN( DATE'2016-04-01', DATE'2016-04-01' - INTERVAL '1' DAY ) AS "MAR-APR", MONTHS_BETWEEN( DATE'2016-05-01', DATE'2016-05-01' - INTERVAL '1' DAY ) AS "APR-MAY" FROM DUAL; Output: JAN-FEB FEB-MAR MAR-APR APR-MAY ------- ------- ------- ------- 0.03226 0.09677 0.03226 0.06452 The difference in years can be found by dividing the month difference by 12. Section 6.4: Extract the Year, Month, Day, Hour, Minute or Second Components of a Date The year, month or day components of a DATE data type can be found using the EXTRACT( [ YEAR | MONTH | DAY ] FROM datevalue ) SELECT EXTRACT (YEAR FROM DATE '2016-07-25') AS YEAR, EXTRACT (MONTH FROM DATE '2016-07-25') AS MONTH, EXTRACT (DAY FROM DATE '2016-07-25') AS DAY FROM DUAL; Outputs: YEAR MONTH DAY ---- ----- --- 2016 7 25 The time (hour, minute or second) components can be found by either: Using CAST( datevalue AS TIMESTAMP ) to convert the DATE to a TIMESTAMP and then using EXTRACT( [ HOUR | MINUTE | SECOND ] FROM timestampvalue ); or Using TO_CHAR( datevalue, format_model ) to get the value as a string. For example: SELECT EXTRACT( HOUR FROM CAST( datetime AS TIMESTAMP ) ) AS Hours, EXTRACT( MINUTE FROM CAST( datetime AS TIMESTAMP ) ) AS Minutes, EXTRACT( SECOND FROM CAST( datetime AS TIMESTAMP ) ) AS Seconds FROM ( SELECT TO_DATE( '2016-01-01 09:42:01', 'YYYY-MM-DD HH24:MI:SS' ) AS datetime FROM DUAL GoalKicker.com – Oracle® Database Notes for Professionals 15 ); Outputs: HOURS MINUTES SECONDS ----- ------- ------- 9 42 1 Section 6.5: Generating Dates with No Time Component All DATEs have a time component; however, it is customary to store dates which do not need to include time information with the hours/minutes/seconds set to zero (i.e. midnight). Use an ANSI DATE literal (using ISO 8601 Date format): SELECT DATE '2000-01-01' FROM DUAL; Convert it from a string literal using TO_DATE(): SELECT TO_DATE( '2001-01-01', 'YYYY-MM-DD' ) FROM DUAL; (More information on the date format models can be found in the Oracle documentation.) or: SELECT TO_DATE( 'January 1, 2000, 00:00 A.M.', 'Month dd, YYYY, HH12:MI A.M.', 'NLS_DATE_LANGUAGE = American' ) FROM DUAL; (If you are converting language specific terms such as month names then it is good practice to include the 3rd nlsparam parameter to the TO_DATE() function and specify the language to be expected.) Section 6.6: Generating Dates with a Time Component Convert it from a string literal using TO_DATE(): SELECT TO_DATE( '2000-01-01 12:00:00', 'YYYY-MM-DD HH24:MI:SS' ) FROM DUAL; Or use a TIMESTAMP literal: CREATE TABLE date_table( date_value DATE ); INSERT INTO date_table ( date_value ) VALUES ( TIMESTAMP '2000-01-01 12:00:00' ); Oracle will implicitly cast a TIMESTAMP to a DATE when storing it in a DATE column of a table; however you can explicitly CAST() the value to a DATE: SELECT CAST( TIMESTAMP '2000-01-01 12:00:00' AS DATE ) FROM DUAL; GoalKicker.com – Oracle® Database Notes for Professionals 16 Section 6.7: The Format of a Date In Oracle a DATE data type does not have a format; when Oracle sends a DATE to the client program (SQL/Plus, SQL/Developer, Toad, Java, Python, etc) it will send 7- or 8- bytes which represent the date. A DATE which is not stored in a table (i.e. generated by SYSDATE and having "type 13" when using the DUMP() command) has 8-bytes and has the structure (the numbers on the right are the internal representation of 2012-11-26 16:41:09): BYTE VALUE EXAMPLE ---- ------------------------------- -------------------------------------- 1 Year modulo 256 220 2 Year multiples of 256 7 (7 * 256 + 220 = 2012) 3 Month 11 4 Day 26 5 Hours 16 6 Minutes 41 7 Seconds 9 8 Unused 0 A DATE which is stored in a table ("type 12" when using the DUMP() command) has 7-bytes and has the structure (the numbers on the right are the internal representation of 2012-11-26 16:41:09): BYTE VALUE EXAMPLE ---- ------------------------------- -------------------------------------- 1 ( Year multiples of 100 ) + 100 120 2 ( Year modulo 100 ) + 100 112 ((120-100)*100 + (112-100) = 2012) 3 Month 11 4 Day 26 5 Hours + 1 17 6 Minutes + 1 42 7 Seconds + 1 10 If you want the date to have a specific format then you will need to convert it to something that has a format (i.e. a string). The SQL client may implicitly do this or you can explicitly convert the value to a string using TO_CHAR( DATE, format_model, nls_params ). Section 6.8: Converting Dates to a String Use TO_CHAR( DATE [, format_model [, nls_params]] ): (Note: if a format model is not provided then the NLS_DATE_FORMAT session parameter will be used as the default format model; this can be different for every session so should not be relied on. It is good practice to always specify the format model.) CREATE TABLE table_name ( date_value DATE ); INSERT INTO table_name ( date_value ) VALUES ( DATE '2000-01-01' ); INSERT INTO table_name ( date_value ) VALUES ( TIMESTAMP '2016-07-21 08:00:00' ); INSERT INTO table_name ( date_value ) VALUES ( SYSDATE ); Then: GoalKicker.com – Oracle® Database Notes for Professionals 17 SELECT TO_CHAR( date_value, 'YYYY-MM-DD' ) AS formatted_date FROM table_name; Outputs: FORMATTED_DATE -------------- 2000-01-01 2016-07-21 2016-07-21 And: SELECT TO_CHAR( date_value, 'FMMonth d yyyy, hh12:mi:ss AM', 'NLS_DATE_LANGUAGE = French' ) AS formatted_date FROM table_name; Outputs: FORMATTED_DATE ----------------------------- Janvier 01 2000, 12:00:00 AM Juillet 21 2016, 08:00:00 AM Juillet 21 2016, 19:08:31 PM Section 6.9: Changing How SQL/Plus or SQL Developer Display Dates When SQL/Plus or SQL Developer display dates they will perform an implicit conversion to a string using the default date format model (see the Setting the Default Date Format Model example). You can change how a date is displayed by changing the NLS_DATE_FORMAT parameter. Section 6.10: Time Zones and Daylight Savings Time The DATE data type does not handle time zones or changes in daylight savings time. Either: use the TIMESTAMP WITH TIME ZONE data type; or handle the changes in your application logic. A DATE can be stored as Coordinated Universal Time (UTC) and converted to the current session time zone like this: SELECT FROM_TZ( CAST( TO_DATE( '2016-01-01 12:00:00', 'YYYY-MM-DD HH24:MI:SS' ) AS TIMESTAMP ), 'UTC' ) AT LOCAL AS TIME GoalKicker.com – Oracle® Database Notes for Professionals 18 FROM DUAL; If you run ALTER SESSION SET TIME_ZONE = '+01:00'; then the output is: TIME ------------------------------------ 2016-01-01 13:00:00.000000000 +01:00 and ALTER SESSION SET TIME_ZONE = 'PST'; then the output is: TIME ------------------------------------ 2016-01-01 04:00:00.000000000 PST Section 6.11: Leap Seconds Oracle does not handle leap seconds. See My Oracle Support note 2019397.2 and 730795.1 for more details. Section 6.12: Getting the Day of the Week You can use TO_CHAR( date_value, 'D' ) to get the day-of-week. However, this is dependent on the NLS_TERRITORY session parameter: ALTER SESSION SET NLS_TERRITORY = 'AMERICA'; -- First day of week is Sunday SELECT TO_CHAR( DATE '1970-01-01', 'D' ) FROM DUAL; Outputs 5 ALTER SESSION SET NLS_TERRITORY = 'UNITED KINGDOM'; -- First day of week is Monday SELECT TO_CHAR( DATE '1970-01-01', 'D' ) FROM DUAL; Outputs 4 To do this independent of the NLS settings, you can truncate the date to midnight of the current day (to remove any fractions of days) and subtract the date truncated to the start of the current iso-week (which always starts on Monday): SELECT TRUNC( date_value ) - TRUNC( date_value, 'IW' ) + 1 FROM DUAL GoalKicker.com – Oracle® Database Notes for Professionals 19 Chapter 7: Working with Dates Section 7.1: Date Arithmetic Oracle supports DATE (includes time to the nearest second) and TIMESTAMP (includes time to fractions of a second) datatypes, which allow arithmetic (addition and subtraction) natively. For example: To get the next day: SELECT TO_CHAR(SYSDATE + 1, 'YYYY-MM-DD') AS tomorrow FROM dual; To get the previous day: SELECT TO_CHAR(SYSDATE - 1, 'YYYY-MM-DD') AS yesterday FROM dual; To add 5 days to the current date: SELECT TO_CHAR(SYSDATE + 5, 'YYYY-MM-DD') AS five_days_from_now FROM dual; To add 5 hours to the current date: SELECT TO_CHAR(SYSDATE + (5/24), 'YYYY-MM-DD HH24:MI:SS') AS five_hours_from_now FROM dual; To add 10 minutes to the current date: SELECT TO_CHAR(SYSDATE + (10/1440), 'YYYY-MM-DD HH24:MI:SS') AS ten_mintues_from_now FROM dual; To add 7 seconds to the current date: SELECT TO_CHAR(SYSDATE + (7/86400), 'YYYY-MM-DD HH24:MI:SS') AS seven_seconds_from_now FROM dual; To select rows where hire_date is 30 days ago or more: SELECT * FROM emp WHERE hire_date < SYSDATE - 30; To select rows where last_updated column is in the last hour: SELECT * FROM logfile WHERE last_updated >= SYSDATE - (1/24); Oracle also provides the built-in datatype INTERVAL which represents a duration of time (e.g. 1.5 days, 36 hours, 2 months, etc.). These can also be used with arithmetic with DATE and TIMESTAMP expressions. For example: SELECT * FROM logfile WHERE last_updated >= SYSDATE - INTERVAL '1' HOUR; Section 7.2: Add_months function Syntax: ADD_MONTHS(p_date, INTEGER) RETURN DATE; Add_months function adds amt months to p_date date. SELECT ADD_MONTHS(DATE'2015-01-12', 2) m FROM dual; M GoalKicker.com – Oracle® Database Notes for Professionals 20 2015-03-12 You can also subtract months using a negative amt SELECT ADD_MONTHS(DATE'2015-01-12', -2) m FROM dual; M 2014-11-12 When the calculated month has fewer days as the given date, the last day of the calculated month will be returned. SELECT TO_CHAR( ADD_MONTHS(DATE'2015-01-31', 1),'YYYY-MM-DD') m FROM dual; M 2015-02-28 GoalKicker.com – Oracle® Database Notes for Professionals 21 Chapter 8: DUAL table Section 8.1: The following example returns the current operating system date and time SELECT SYSDATE FROM dual Section 8.2: The following example generates numbers between start_value and end_value SELECT :start_value + LEVEL -1 n FROM dual CONNECT BY LEVEL <= :end_value - :start_value + 1 GoalKicker.com – Oracle® Database Notes for Professionals 22 Chapter 9: JOINS Section 9.1: CROSS JOIN A CROSS JOIN performs a join between two tables that does not use an explicit join clause and results in the Cartesian product of two tables. A Cartesian product means each row of one table is combined with each row of the second table in the join. For example, if TABLEA has 20 rows and TABLEB has 20 rows, the result would be 20*20 = 400 output rows. Example: SELECT * FROM TABLEA CROSS JOIN TABLEB; This can also be written as: SELECT * FROM TABLEA, TABLEB; Here's an example of cross join in SQL between two tables: Sample Table: TABLEA +-------+---------+ | VALUE | NAME | +-------+---------+ | 1 | ONE | | 2 | TWO | +-------+---------+ Sample Table: TABLEB +-------+--------+ | VALUE | NAME | +-------+--------+ | 3 | THREE | | 4 | FOUR | +-------+--------+ Now, If you execute the query: SELECT * FROM TABLEA CROSS JOIN TABLEB; Output: +-------+--------+-------+--------+ | VALUE | NAME | VALUE | NAME | +-------+--------+-------+--------+ | 1 | ONE | 3 | THREE | | 1 | ONE | 4 | FOUR | | 2 | TWO | 3 | THREE | | 2 | TWO | 4 | FOUR | GoalKicker.com – Oracle® Database Notes for Professionals 23 +-------+--------+-------+--------+ This is how cross joining happens between two tables: More about Cross Join: Oracle documentation Section 9.2: LEFT OUTER JOIN A LEFT OUTER JOIN performs a join between two tables that requires an explicit join clause but does not exclude unmatched rows from the first table. Example: SELECT ENAME, DNAME, EMP.DEPTNO, DEPT.DEPTNO FROM SCOTT.EMP LEFT OUTER JOIN SCOTT.DEPT ON EMP.DEPTNO = DEPT.DEPTNO; Even though ANSI syntax is the recommended way, it is likely to encounter legacy syntax very often. Using (+) within a condition determines which side of the equation to be considered as outer. SELECT ENAME, DNAME, EMP.DEPTNO, DEPT.DEPTNO FROM SCOTT.EMP, SCOTT.DEPT WHERE EMP.DEPTNO = DEPT.DEPTNO(+); Here's an example of Left Outer Join between two tables: Sample Table: EMPLOYEE +-----------+---------+ | NAME | DEPTNO | +-----------+---------+ | A | 2 | | B | 1 | | C | 3 | | D | 2 | | E | 1 | | F | 1 | | G | 4 | | H | 4 | GoalKicker.com – Oracle® Database Notes for Professionals 24 +-----------+---------+ Sample Table: DEPT +---------+--------------+ | DEPTNO | DEPTNAME | +---------+--------------+ | 1 | ACCOUNTING | | 2 | FINANCE | | 5 | MARKETING | | 6 | HR | +---------+--------------+ Now, If you execute the query: SELECT * FROM EMPLOYEE LEFT OUTER JOIN DEPT ON EMPLOYEE.DEPTNO = DEPT.DEPTNO; Output: +-----------+---------+---------+--------------+ | NAME | DEPTNO | DEPTNO | DEPTNAME | +-----------+---------+---------+--------------+ | F | 1 | 1 | ACCOUNTING | | E | 1 | 1 | ACCOUNTING | | B | 1 | 1 | ACCOUNTING | | D | 2 | 2 | FINANCE | | A | 2 | 2 | FINANCE | | C | 3 | | | | H | 4 | | | | G | 4 | | | +-----------+---------+---------+--------------+ Section 9.3: RIGHT OUTER JOIN A RIGHT OUTER JOIN performs a join between two tables that requires an explicit join clause but does not exclude unmatched rows from the second table. Example: SELECT ENAME, DNAME, EMP.DEPTNO, DEPT.DEPTNO FROM SCOTT.EMP RIGHT OUTER JOIN SCOTT.DEPT ON EMP.DEPTNO = DEPT.DEPTNO; As the unmatched rows of SCOTT.DEPT are included, but unmatched rows of SCOTT.EMP are not, the above is equivalent to the following statement using LEFT OUTER JOIN. GoalKicker.com – Oracle® Database Notes for Professionals 25 SELECT ENAME, DNAME, EMP.DEPTNO, DEPT.DEPTNO FROM SCOTT.DEPT RIGHT OUTER JOIN SCOTT.EMP ON DEPT.DEPTNO = EMP.DEPTNO; Here's an example of Right Outer Join between two tables: Sample Table: EMPLOYEE +-----------+---------+ | NAME | DEPTNO | +-----------+---------+ | A | 2 | | B | 1 | | C | 3 | | D | 2 | | E | 1 | | F | 1 | | G | 4 | | H | 4 | +-----------+---------+ Sample Table: DEPT +---------+--------------+ | DEPTNO | DEPTNAME | +---------+--------------+ | 1 | ACCOUNTING | | 2 | FINANCE | | 5 | MARKETING | | 6 | HR | +---------+--------------+ Now, If you execute the query: SELECT * FROM EMPLOYEE RIGHT OUTER JOIN DEPT ON EMPLOYEE.DEPTNO = DEPT.DEPTNO; Output: +-----------+---------+---------+--------------+ | NAME | DEPTNO | DEPTNO | DEPTNAME | +-----------+---------+---------+--------------+ | A | 2 | 2 | FINANCE | | B | 1 | 1 | ACCOUNTING | | D | 2 | 2 | FINANCE | | E | 1 | 1 | ACCOUNTING | | F | 1 | 1 | ACCOUNTING | | | | 5 | MARKETING | | | | 6 | HR | GoalKicker.com – Oracle® Database Notes for Professionals 26 +-----------+---------+---------+--------------+ Oracle (+) syntax equivalent for the query is: SELECT * FROM EMPLOYEE, DEPT WHERE EMPLOYEE.DEPTNO(+) = DEPT.DEPTNO; Section 9.4: FULL OUTER JOIN A FULL OUTER JOIN performs a join between two tables that requires an explicit join clause but does not exclude unmatched rows in either table. In other words, it returns all the rows in each table. Example: SELECT * FROM EMPLOYEE FULL OUTER JOIN DEPT ON EMPLOYEE.DEPTNO = DEPT.DEPTNO; Here's an example of Full Outer Join between two tables: Sample Table: EMPLOYEE +-----------+---------+ | NAME | DEPTNO | +-----------+---------+ | A | 2 | | B | 1 | | C | 3 | | D | 2 | | E | 1 | | F | 1 | | G | 4 | | H | 4 | +-----------+---------+ Sample Table: DEPT +---------+--------------+ | DEPTNO | DEPTNAME | +---------+--------------+ | 1 | ACCOUNTING | | 2 | FINANCE | | 5 | MARKETING | | 6 | HR | +---------+--------------+ Now, If you execute the query: SELECT * FROM EMPLOYEE FULL OUTER JOIN DEPT GoalKicker.com – Oracle® Database Notes for Professionals 27 ON EMPLOYEE.DEPTNO = DEPT.DEPTNO; Output +-----------+---------+---------+--------------+ | NAME | DEPTNO | DEPTNO | DEPTNAME | +-----------+---------+---------+--------------+ | A | 2 | 2 | FINANCE | | B | 1 | 1 | ACCOUNTING | | C | 3 | | | | D | 2 | 2 | FINANCE | | E | 1 | 1 | ACCOUNTING | | F | 1 | 1 | ACCOUNTING | | G | 4 | | | | H | 4 | | | | | | 6 | HR | | | | 5 | MARKETING | +-----------+---------+---------+--------------+ Here the columns that do not match has been kept NULL. Section 9.5: ANTIJOIN An antijoin returns rows from the left side of the predicate for which there are no corresponding rows on the right side of the predicate. It returns rows that fail to match (NOT IN) the subquery on the right side. SELECT * FROM employees WHERE department_id NOT IN (SELECT department_id FROM departments WHERE location_id = 1700) ORDER BY last_name; Here's an example of Anti Join between two tables: Sample Table: EMPLOYEE +-----------+---------+ | NAME | DEPTNO | +-----------+---------+ | A | 2 | | B | 1 | | C | 3 | | D | 2 | | E | 1 | | F | 1 | | G | 4 | | H | 4 | +-----------+---------+ Sample Table: DEPT +---------+--------------+ | DEPTNO | DEPTNAME | +---------+--------------+ | 1 | ACCOUNTING | | 2 | FINANCE | GoalKicker.com – Oracle® Database Notes for Professionals 28 | 5 | MARKETING | | 6 | HR | +---------+--------------+ Now, If you execute the query: SELECT * FROM EMPLOYEE WHERE DEPTNO NOT IN (SELECT DEPTNO FROM DEPT); Output: +-----------+---------+ | NAME | DEPTNO | +-----------+---------+ | C | 3 | | H | 4 | | G | 4 | +-----------+---------+ The output shows that only the rows of EMPLOYEE table, of which DEPTNO were not present in DEPT table. Section 9.6: INNER JOIN An INNER JOIN is a JOIN operation that allows you to specify an explicit join clause. Syntax TableExpression [ INNER ] JOIN TableExpression { ON booleanExpression | USING clause } You can specify the join clause by specifying ON with a boolean expression. The scope of expressions in the ON clause includes the current tables and any tables in outer query blocks to the current SELECT. In the following example, the ON clause refers to the current tables: -- Join the EMP_ACT and EMPLOYEE tables -- select all the columns from the EMP_ACT table and -- add the employee's surname (LASTNAME) from the EMPLOYEE table -- to each row of the result SELECT SAMP.EMP_ACT.*, LASTNAME FROM SAMP.EMP_ACT JOIN SAMP.EMPLOYEE ON EMP_ACT.EMPNO = EMPLOYEE.EMPNO -- Join the EMPLOYEE and DEPARTMENT tables, -- select the employee number (EMPNO), -- employee surname (LASTNAME), -- department number (WORKDEPT in the EMPLOYEE table and DEPTNO in the -- DEPARTMENT table) -- and department name (DEPTNAME) -- of all employees who were born (BIRTHDATE) earlier than 1930. SELECT EMPNO, LASTNAME, WORKDEPT, DEPTNAME FROM SAMP.EMPLOYEE JOIN SAMP.DEPARTMENT ON WORKDEPT = DEPTNO AND YEAR(BIRTHDATE) < 1930 -- Another example of "generating" new data values, GoalKicker.com – Oracle® Database Notes for Professionals 29 -- using a query which selects from a VALUES clause (which is an -- alternate form of a fullselect). -- This query shows how a table can be derived called "X" -- having 2 columns "R1" and "R2" and 1 row of data SELECT * FROM (VALUES (3, 4), (1, 5), (2, 6)) AS VALUESTABLE1(C1, C2) JOIN (VALUES (3, 2), (1, 2), (0, 3)) AS VALUESTABLE2(c1, c2) ON VALUESTABLE1.c1 = VALUESTABLE2.c1 -- This results in: -- C1 |C2 |C1 |2 -- ----------------------------------------------- -- 3 |4 |3 |2 -- 1 |5 |1 |2 -- List every department with the employee number and -- last name of the manager SELECT DEPTNO, DEPTNAME, EMPNO, LASTNAME FROM DEPARTMENT INNER JOIN EMPLOYEE ON MGRNO = EMPNO -- List every employee number and last name -- with the employee number and last name of their manager SELECT E.EMPNO, E.LASTNAME, M.EMPNO, M.LASTNAME FROM EMPLOYEE E INNER JOIN DEPARTMENT INNER JOIN EMPLOYEE M ON MGRNO = M.EMPNO ON E.WORKDEPT = DEPTNO Section 9.7: JOIN The JOIN operation performs a join between two tables, excluding any unmatched rows from the first table. From Oracle 9i forward, the JOIN is equivalent in function to the INNER JOIN. This operation requires an explicit join clause, as opposed to the CROSS JOIN and NATURAL JOIN operators. Example: SELECT t1.*, t2.DeptId FROM table_1 t1 JOIN table_2 t2 ON t2.DeptNo = t1.DeptNo Oracle documentation: 10g 11g 12g Section 9.8: SEMIJOIN A semijoin query can be used, for example, to find all departments with at least one employee whose salary exceeds 2500. SELECT * FROM departments WHERE EXISTS GoalKicker.com – Oracle® Database Notes for Professionals 30 (SELECT 1 FROM employees WHERE departments.department_id = employees.department_id AND employees.salary > 2500) ORDER BY department_name; This is more efficient than the full join alternatives, as inner joining on employees then giving a where clause detailing that the salary has to be greater than 2500 could return the same department numerous times. Say if the Fire department has n employees all with salary 3000, SELECT * FROM departments, employees with the necessary join on ids and our where clause would return the Fire department n times. Section 9.9: NATURAL JOIN NATURAL JOIN requires no explitic join condition; it builds one based on all the fields with the same name in the joined tables. CREATE TABLE tab1(id NUMBER, descr VARCHAR2(100)); CREATE TABLE tab2(id NUMBER, descr VARCHAR2(100)); INSERT INTO tab1 VALUES(1, 'one'); INSERT INTO tab1 VALUES(2, 'two'); INSERT INTO tab1 VALUES(3, 'three'); INSERT INTO tab2 VALUES(1, 'ONE'); INSERT INTO tab2 VALUES(3, 'three'); The join will be done on the fields ID and DESCR, common to both the tables: SQL> SELECT * 2 FROM tab1 3 NATURAL JOIN 4 tab2; ID DESCR ---------- ---------- 3 three Columns with different names will not be used in the JOIN condition: SQL> SELECT * 2 FROM (SELECT id AS id, descr AS descr1 FROM tab1) 3 NATURAL JOIN 4 (SELECT id AS id, descr AS descr2 FROM tab2); ID DESCR1 DESCR2 ---------- ---------- ---------- 1 one ONE 3 three three If the joined tables have no common columns, a JOIN with no conditions will be done: SQL> SELECT * 2 FROM (SELECT id AS id1, descr AS descr1 FROM tab1) 3 NATURAL JOIN 4 (SELECT id AS id2, descr AS descr2 FROM tab2); ID1 DESCR1 ID2 DESCR2 ---------- ---------- ---------- ---------- GoalKicker.com – Oracle® Database Notes for Professionals 31 1 one 1 ONE 2 two 1 ONE 3 three 1 ONE 1 one 3 three 2 two 3 three 3 three 3 three GoalKicker.com – Oracle® Database Notes for Professionals 32 Chapter 10: Handling NULL values A column is NULL when it has no value, regardless of the data type of that column. A column should never be compared to NULL using this syntax a = NULL as the result would be UNKNOWN. Instead use a IS NULL or a IS NOT NULL conditions. NULL is not equal to NULL. To compare two expressions where null can happen, use one of the functions described below. All operators except concatenation return NULL if one of their operand is NULL. For instance the result of 3 * NULL + 5 is null. Section 10.1: Operations containing NULL are NULL, except concatenation SELECT 3 * NULL + 5, 'Hello ' || NULL || 'world' FROM DUAL; 3*NULL+5 'HELLO'||NULL||'WORLD' (null) Hello world Section 10.2: NVL2 to get a dierent result if a value is null or not If the first parameter is NOT NULL, NVL2 will return the second parameter. Otherwise it will return the third one. SELECT NVL2(NULL, 'Foo', 'Bar'), NVL2(5, 'Foo', 'Bar') FROM DUAL; NVL2(NULL,'FOO','BAR') NVL2(5,'FOO','BAR') Bar Foo Section 10.3: COALESCE to return the first non-NULL value SELECT COALESCE(a, b, c, d, 5) FROM (SELECT NULL A, NULL b, NULL c, 4 d FROM DUAL); COALESCE(A,B,C,D,5) 4 In some case, using COALESCE with two parameters can be faster than using NVL when the second parameter is not a constant. NVL will always evaluate both parameters. COALESCE will stop at the first non-NULL value it encounters. It means that if the first value is non-NULL, COALESCE will be faster. Section 10.4: Columns of any data type can contain NULLs SELECT 1 NUM_COLUMN, 'foo' VARCHAR2_COLUMN FROM DUAL UNION ALL SELECT NULL, NULL FROM DUAL; NUM_COLUMN VARCHAR2_COLUMN 1 foo (null) (null) Section 10.5: Empty strings are NULL SELECT 1 a, '' b FROM DUAL; A B 1 (null) GoalKicker.com – Oracle® Database Notes for Professionals 33 Section 10.6: NVL to replace null value SELECT a column_with_null, NVL(a, 'N/A') column_without_null FROM (SELECT NULL a FROM DUAL); COLUMN_WITH_NULL COLUMN_WITHOUT_NULL (null) N/A NVL is useful to compare two values which can contain NULLs : SELECT CASE WHEN a = b THEN 1 WHEN a <> b THEN 0 ELSE -1 END comparison_without_nvl, CASE WHEN NVL(a, -1) = NVL(b, -1) THEN 1 WHEN NVL(a, -1) <> NVL(b, -1) THEN 0 ELSE -1 END comparison_with_nvl FROM (SELECT NULL a, 3 b FROM DUAL UNION ALL SELECT NULL, NULL FROM DUAL); COMPARISON_WITHOUT_NVL COMPARISON_WITH_NVL -1 0 -1 1 GoalKicker.com – Oracle® Database Notes for Professionals 34 Chapter 11: String Manipulation Section 11.1: INITCAP The INITCAP function converts the case of a string so that each word starts with a capital letter and all subsequent letters are in lowercase. SELECT INITCAP('HELLO mr macdonald!') AS NEW FROM dual; Output NEW ------------------- Hello Mr Macdonald! Section 11.2: Regular expression Let's say we want to replace only numbers with 2 digits: regular expression will find them with (\d\d) SELECT REGEXP_REPLACE ('2, 5, and 10 are numbers in this example', '(\d\d)', '#') FROM dual; Results in: '2, 5, and # are numbers in this example' If I want to swap parts of the text, I use \1, \2, \3 to call for the matched strings: SELECT REGEXP_REPLACE ('swap around 10 in that one ', '(.*)(\d\d )(.*)', '\3\2\1\3') FROM dual; Section 11.3: SUBSTR SUBSTR retrieves part of a string by indicating the starting position and the number of characters to extract SELECT SUBSTR('abcdefg',2,3) FROM DUAL; returns: bcd To count from the end of the string, SUBSTR accepts a negative number as the second parameter, e.g. SELECT SUBSTR('abcdefg',-4,2) FROM DUAL; returns: de To get the last character in a string: SUBSTR(mystring,-1,1) GoalKicker.com – Oracle® Database Notes for Professionals 35 Section 11.4: Concatenation: Operator || or concat() function The Oracle SQL and PL/SQL || operator allows you to concatenate 2 or more strings together. Example: Assuming the following customers table: id firstname lastname --- ----------- ---------- 1 Thomas Woody Query: SELECT firstname || ' ' || lastname || ' is in my database.' AS "My Sentence" FROM customers; Output: My Sentence --------------------------------- Thomas Woody is in my database. Oracle also supports the standard SQL CONCAT(str1, str2) function: Example: Query: SELECT CONCAT(firstname, ' is in my database.') FROM customers; Output: Expr1 --------------------------------- Thomas is in my database. Section 11.5: UPPER The UPPER function allows you to convert all lowercase letters in a string to uppercase. SELECT UPPER('My text 123!') AS result FROM dual; Output: RESULT ------------ MY TEXT 123! GoalKicker.com – Oracle® Database Notes for Professionals 36 Section 11.6: LOWER LOWER converts all uppercase letters in a string to lowercase. SELECT LOWER('HELLO World123!') text FROM dual; Outputs: text hello world123! Section 11.7: LTRIM / RTRIM LTRIM and RTRIM remove characters from the beginning or the end (respectively) of a string. A set of one or more characters may be supplied (default is a space) to remove. For example, SELECT LTRIM('<===>HELLO<===>', '=<>') ,RTRIM('<===>HELLO<===>', '=<>') FROM dual; Returns: HELLO<===> <===>HELLO GoalKicker.com – Oracle® Database Notes for Professionals 37 Chapter 12: IF-THEN-ELSE Statement Section 12.1: IF-THEN DECLARE v_num1 NUMBER(10); v_num2 NUMBER(10); BEGIN v_num1 := 2; v_num2 := 1; IF v_num1 > v_num2 THEN DBMS_OUTPUT.put_line('v_num1 is bigger than v_num2'); END IF; END; Section 12.2: IF-THEN-ELSE DECLARE v_num1 NUMBER(10); v_num2 NUMBER(10); BEGIN v_num1 := 2; v_num2 := 10; IF v_num1 > v_num2 THEN DBMS_OUTPUT.put_line('v_num1 is bigger than v_num2'); ELSE DBMS_OUTPUT.put_line('v_num1 is NOT bigger than v_num2'); END IF; END; Section 12.3: IF-THEN-ELSIF-ELSE DECLARE v_num1 NUMBER(10); v_num2 NUMBER(10); BEGIN v_num1 := 2; v_num2 := 2; IF v_num1 > v_num2 THEN DBMS_OUTPUT.put_line('v_num1 is bigger than v_num2'); ELSIF v_num1 < v_num2 THEN DBMS_OUTPUT.put_line('v_num1 is NOT bigger than v_num2'); ELSE DBMS_OUTPUT.put_line('v_num1 is EQUAL to v_num2'); END IF; END; GoalKicker.com – Oracle® Database Notes for Professionals 38 Chapter 13: Limiting the rows returned by a query (Pagination) Section 13.1: Get first N rows with row limiting clause The FETCH clause was introduced in Oracle 12c R1: SELECT val FROM mytable ORDER BY val DESC FETCH FIRST 5 ROWS ONLY; An example without FETCH that works also in earlier versions: SELECT * FROM ( SELECT val FROM mytable ORDER BY val DESC ) WHERE ROWNUM <= 5; Section 13.2: Get row N through M from many rows (before Oracle 12c) Use the analytical function row_number(): WITH t AS ( SELECT col1 , col2 , ROW_NUMBER() over (ORDER BY col1, col2) rn FROM TABLE ) SELECT col1 , col2 FROM t WHERE rn BETWEEN N AND M; -- N and M are both inclusive Oracle 12c handles this more easily with OFFSET and FETCH. Section 13.3: Get N numbers of Records from table We can limit no of rows from result using rownum clause SELECT * FROM ( SELECT val FROM mytable ) WHERE rownum<=5 If we want first or last record then we want order by clause in inner query that will give result based on order. Last Five Record : SELECT * FROM ( SELECT val FROM mytable ORDER BY val DESC GoalKicker.com – Oracle® Database Notes for Professionals 39 ) WHERE rownum<=5 First Five Record SELECT * FROM ( SELECT val FROM mytable ORDER BY val ) WHERE rownum<=5 Section 13.4: Skipping some rows then taking some In Oracle 12g+ SELECT Id, Col1 FROM TableName ORDER BY Id OFFSET 20 ROWS FETCH NEXT 20 ROWS ONLY; In earlier Versions SELECT Id, Col1 FROM (SELECT Id, Col1, ROW_NUMBER() over (ORDER BY Id) RowNumber FROM TableName) WHERE RowNumber BETWEEN 21 AND 40 Section 13.5: Skipping some rows from result In Oracle 12g+ SELECT Id, Col1 FROM TableName ORDER BY Id OFFSET 5 ROWS; In earlier Versions SELECT Id, Col1 FROM (SELECT Id, Col1, ROW_NUMBER() over (ORDER BY Id) RowNumber FROM TableName) WHERE RowNumber > 20 Section 13.6: Pagination in SQL SELECT val FROM (SELECT val, ROWNUM AS rnum FROM (SELECT val FROM rownum_order_test ORDER BY val) WHERE ROWNUM <= :upper_limit) WHERE rnum >= :lower_limit ; GoalKicker.com – Oracle® Database Notes for Professionals 40 this way we can paginate the table data , just like web serch page GoalKicker.com – Oracle® Database Notes for Professionals 41 Chapter 14: Recursive Sub-Query Factoring using the WITH Clause (A.K.A. Common Table Expressions) Section 14.1: Splitting a Delimited String Sample Data: CREATE TABLE table_name ( VALUE VARCHAR2(50) ); INSERT INTO table_name ( VALUE ) VALUES ( 'A,B,C,D,E' ); Query: WITH items ( list, item, lvl ) AS ( SELECT VALUE, REGEXP_SUBSTR( VALUE, '[^,]+', 1, 1 ), 1 FROM table_name UNION ALL SELECT VALUE, REGEXP_SUBSTR( VALUE, '[^,]+', 1, lvl + 1 ), lvl + 1 FROM items WHERE lvl < REGEXP_COUNT( VALUE, '[^,]+' ) ) SELECT * FROM items; Output: LIST ITEM LVL --------- ---- --- A,B,C,D,E A 1 A,B,C,D,E B 2 A,B,C,D,E C 3 A,B,C,D,E D 4 A,B,C,D,E E 5 Section 14.2: A Simple Integer Generator Query: WITH generator ( VALUE ) AS ( SELECT 1 FROM DUAL UNION ALL SELECT VALUE + 1 FROM generator WHERE VALUE < 10 ) SELECT VALUE FROM generator; Output: GoalKicker.com – Oracle® Database Notes for Professionals 42 VALUE ----- 1 2 3 4 5 6 7 8 9 10 GoalKicker.com – Oracle® Database Notes for Professionals 43 Chapter 15: Dierent ways to update records Section 15.1: Update using Merge Using Merge MERGE INTO TESTTABLE USING (SELECT T1.ROWID AS RID, T2.TESTTABLE_ID FROM TESTTABLE T1 INNER JOIN MASTERTABLE T2 ON TESTTABLE.TESTTABLE_ID = MASTERTABLE.TESTTABLE_ID WHERE ID_NUMBER=11) ON ( ROWID = RID ) WHEN MATCHED THEN UPDATE SET TEST_COLUMN= 'Testvalue'; Section 15.2: Update Syntax with example Normal Update UPDATE TESTTABLE SET TEST_COLUMN= 'Testvalue',TEST_COLUMN2= 123 WHERE EXISTS (SELECT MASTERTABLE.TESTTABLE_ID FROM MASTERTABLE WHERE ID_NUMBER=11); Section 15.3: Update Using Inline View Using Inline View (If it is considered updateable by Oracle) Note: If you face a non key preserved row error add an index to resolve the same to make it update-able UPDATE (SELECT TESTTABLE.TEST_COLUMN AS OLD, 'Testvalue' AS NEW FROM TESTTABLE INNER JOIN MASTERTABLE ON TESTTABLE.TESTTABLE_ID = MASTERTABLE.TESTTABLE_ID WHERE ID_NUMBER=11) T SET GoalKicker.com – Oracle® Database Notes for Professionals 44 T.OLD = T.NEW; Section 15.4: Merge with sample data DROP TABLE table01; DROP TABLE table02; CREATE TABLE table01 ( code int, name VARCHAR(50), old int ); CREATE TABLE table02 ( code int, name VARCHAR(50), old int ); truncate TABLE table01; INSERT INTO table01 VALUES (1, 'A', 10); INSERT INTO table01 VALUES (9, 'B', 12); INSERT INTO table01 VALUES (3, 'C', 14); INSERT INTO table01 VALUES (4, 'D', 16); INSERT INTO table01 VALUES (5, 'E', 18); truncate TABLE table02; INSERT INTO table02 VALUES (1, 'AA', NULL); INSERT INTO table02 VALUES (2, 'BB', 123); INSERT INTO table02 VALUES (3, 'CC', NULL); INSERT INTO table02 VALUES (4, 'DD', NULL); INSERT INTO table02 VALUES (5, 'EE', NULL); SELECT * FROM table01 a ORDER BY 2; SELECT * FROM table02 a ORDER BY 2; -- MERGE INTO table02 a USING ( SELECT b.code, b.old FROM table01 b ) c ON ( a.code = c.code ) WHEN matched THEN UPDATE SET a.old = c.old ; -- SELECT a.*, b.* FROM table01 a inner JOIN table02 b ON a.code = b.codetable01; SELECT * FROM table01 a WHERE EXISTS ( SELECT 'x' FROM table02 b WHERE a.code = b.codetable01 ); SELECT * FROM table01 a WHERE a.code IN (SELECT b.codetable01 FROM table02 b); -- GoalKicker.com – Oracle® Database Notes for Professionals 45 SELECT * FROM table01 a WHERE NOT EXISTS ( SELECT 'x' FROM table02 b WHERE a.code = b.codetable01 ); SELECT * FROM table01 a WHERE a.code NOT IN (SELECT b.codetable01 FROM table02 b); GoalKicker.com – Oracle® Database Notes for Professionals 46 Chapter 16: Update with Joins Contrary to widespread misunderstanding (including on SO), Oracle allows updates through joins. However, there are some (pretty logical) requirements. We illustrate what doesn't work and what does through a simple example. Another way to achieve the same is the MERGE statement. Section 16.1: Examples: what works and what doesn't CREATE TABLE tgt ( id, val ) AS SELECT 1, 'a' FROM dual UNION ALL SELECT 2, 'b' FROM dual ; TABLE TGT created. CREATE TABLE src ( id, val ) AS SELECT 1, 'x' FROM dual UNION ALL SELECT 2, 'y' FROM dual ; TABLE SRC created. UPDATE ( SELECT t.val AS t_val, s.val AS s_val FROM tgt t inner JOIN src s ON t.id = s.id ) SET t_val = s_val ; SQL Error: ORA-01779: cannot modify a column which maps to a non key-preserved table 01779. 00000 - "cannot modify a column which maps to a non key-preserved table" *Cause: An attempt was made to insert or update columns of a join view which map to a non-key-preserved table. *Action: Modify the underlying base tables directly. Imagine what would happen if we had the value 1 in the column src.id more than once, with different values for src.val. Obviously, the update would make no sense (in ANY database - that's a logical issue). Now, we know that there are no duplicates in src.id, but the Oracle engine doesn't know that - so it's complaining. Perhaps this is why so many practitioners believe Oracle "doesn't have UPDATE with joins"? What Oracle expects is that src.id should be unique, and that it, Oracle, would know that beforehand. Easily fixed! Note that the same works with composite keys (on more than one column), if the matching for the update needs to use more than one column. In practice, src.id may be PK and tgt.id may be FK pointing to this PK, but that is not relevant for updates with join; what is relevant is the unique constraint. ALTER TABLE src ADD constraint src_uc UNIQUE (id); TABLE SRC altered. UPDATE ( SELECT t.val AS t_val, s.val AS s_val FROM tgt t inner JOIN src s ON t.id = s.id ) SET t_val = s_val ; GoalKicker.com – Oracle® Database Notes for Professionals 47 2 rows updated. SELECT * FROM tgt; ID VAL -- --- 1 x 2 y The same result could be achieved with a MERGE statement (which deserves its own Documentation article), and I personally prefer MERGE in these cases, but the reason is not that "Oracle doesn't do updates with joins." As this example shows, Oracle does do updates with joins. GoalKicker.com – Oracle® Database Notes for Professionals 48 Chapter 17: Functions Section 17.1: Calling Functions There are a few ways to use functions. Calling a function with an assignment statement DECLARE x NUMBER := functionName(); --functions can be called in declaration section BEGIN x := functionName(); END; Calling a function in IF statement IF functionName() = 100 THEN NULL; END IF; Calling a function in a SELECT statement SELECT functionName() FROM DUAL; GoalKicker.com – Oracle® Database Notes for Professionals 49 Chapter 18: Statistical functions Section 18.1: Calculating the median of a set of values The MEDIAN function since Oracle 10g is an easy to use aggregation function: SELECT MEDIAN(SAL) FROM EMP It returns the median of the values Works on DATETIME values too. The result of MEDIAN is computed by first ordering the rows. Using N as the number of rows in the group, Oracle calculates the row number (RN) of interest with the formula RN = (1 + (0.5*(N-1)). The final result of the aggregate function is computed by linear interpolation between the values from rows at row numbers CRN = CEILING(RN) and FRN = FLOOR(RN). Since Oracle 9i you can use PERCENTILE_CONT which works the same as MEDIAN function with percentile value defaults to 0.5 SELECT PERCENTILE_CONT(.5) WITHIN GROUP(ORDER BY SAL) FROM EMP GoalKicker.com – Oracle® Database Notes for Professionals 50 Chapter 19: Window Functions Section 19.1: Ratio_To_Report Provides the ratio of the current rows value to all the values within the window. --Data CREATE TABLE Employees (Name VARCHAR2(30), Salary NUMBER(10)); INSERT INTO Employees VALUES ('Bob',2500); INSERT INTO Employees VALUES ('Alice',3500); INSERT INTO Employees VALUES ('Tom',2700); INSERT INTO Employees VALUES ('Sue',2000); --Query SELECT Name, Salary, RATIO_TO_REPORT(Salary) OVER () AS Ratio FROM Employees ORDER BY Salary, Name, Ratio; --Output NAME SALARY RATIO ------------------------------ ---------- ---------- Sue 2000 .186915888 Bob 2500 .23364486 Tom 2700 .252336449 Alice 3500 .327102804 GoalKicker.com – Oracle® Database Notes for Professionals 51 Chapter 20: Creating a Context Parameter Details OR REPLACE Redefine an existing context namespace namespace Name of the context - this is the namespace for calls to SYS_CONTEXT schema Owner of the package package Database package that sets or resets the context attributes. Note: the database package doesn't have to exist in order to create the context. INITIALIZED Specify an entity other than Oracle Database that can set the context. EXTERNALLY Allow the OCI interface to initialize the context. GLOBALLY Allow the LDAP directory to initialize the context when establishing the session. ACCESSED GLOBALLY Allow the context to be accessible throughout the entire instance - multiple sessions can share the attribute values as long as they have the same Client ID. Section 20.1: Create a Context CREATE CONTEXT my_ctx USING my_pkg; This creates a context that can only be set by routines in the database package my_pkg, e.g.: CREATE PACKAGE my_pkg AS PROCEDURE set_ctx; END my_pkg; CREATE PACKAGE BODY my_pkg AS PROCEDURE set_ctx IS BEGIN DBMS_SESSION.set_context('MY_CTX','THE KEY','Value'); DBMS_SESSION.set_context('MY_CTX','ANOTHER','Bla'); END set_ctx; END my_pkg; Now, if a session does this: my_pkg.set_ctx; It can now retrieve the value for the key thus: SELECT SYS_CONTEXT('MY_CTX','THE KEY') FROM dual; VALUE GoalKicker.com – Oracle® Database Notes for Professionals 52 Chapter 21: Splitting Delimited Strings Section 21.1: Splitting Strings using a Hierarchical Query Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: SELECT t.id, REGEXP_SUBSTR( list, '([^,]*)(,|$)', 1, LEVEL, NULL, 1 ) AS VALUE, LEVEL AS lvl FROM table_name t CONNECT BY id = PRIOR id AND PRIOR SYS_GUID() IS NOT NULL AND LEVEL < REGEXP_COUNT( list, '([^,]*)(,|$)' ) Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 Section 21.2: Splitting Strings using a PL/SQL Function PL/SQL Function: CREATE OR REPLACE FUNCTION split_String( i_str IN VARCHAR2, i_delim IN VARCHAR2 DEFAULT ',' ) RETURN SYS.ODCIVARCHAR2LIST DETERMINISTIC AS p_result SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST(); p_start NUMBER(5) := 1; p_end NUMBER(5); c_len CONSTANT NUMBER(5) := LENGTH( i_str ); c_ld CONSTANT NUMBER(5) := LENGTH( i_delim ); BEGIN IF c_len > 0 THEN p_end := INSTR( i_str, i_delim, p_start ); WHILE p_end > 0 LOOP p_result.EXTEND; GoalKicker.com – Oracle® Database Notes for Professionals 53 p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, p_end - p_start ); p_start := p_end + c_ld; p_end := INSTR( i_str, i_delim, p_start ); END LOOP; IF p_start <= c_len + 1 THEN p_result.EXTEND; p_result( p_result.COUNT ) := SUBSTR( i_str, p_start, c_len - p_start + 1 ); END IF; END IF; RETURN p_result; END; / Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: SELECT t.id, v.column_value AS VALUE, ROW_NUMBER() OVER ( PARTITION BY id ORDER BY ROWNUM ) AS lvl FROM table_name t, TABLE( split_String( t.list ) ) (+) v Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 Section 21.3: Splitting Strings using a Recursive Sub-query Factoring Clause Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: WITH bounds ( id, list, start_pos, end_pos, lvl ) AS ( GoalKicker.com – Oracle® Database Notes for Professionals 54 SELECT id, list, 1, INSTR( list, ',' ), 1 FROM table_name UNION ALL SELECT id, list, end_pos + 1, INSTR( list, ',', end_pos + 1 ), lvl + 1 FROM bounds WHERE end_pos > 0 ) SELECT id, SUBSTR( list, start_pos, CASE end_pos WHEN 0 THEN LENGTH( list ) + 1 ELSE end_pos END - start_pos ) AS item, lvl FROM bounds ORDER BY id, lvl; Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 Section 21.4: Splitting Strings using a Correlated Table Expression Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: SELECT t.id, v.COLUMN_VALUE AS VALUE, ROW_NUMBER() OVER ( PARTITION BY id ORDER BY ROWNUM ) AS lvl FROM table_name t, TABLE( CAST( MULTISET( GoalKicker.com – Oracle® Database Notes for Professionals 55 SELECT REGEXP_SUBSTR( t.list, '([^,]*)(,|$)', 1, LEVEL, NULL, 1 ) FROM DUAL CONNECT BY LEVEL < REGEXP_COUNT( t.list, '[^,]*(,|$)' ) ) AS SYS.ODCIVARCHAR2LIST ) ) v; Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 Section 21.5: Splitting Strings using CROSS APPLY (Oracle 12c) Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: SELECT t.id, REGEXP_SUBSTR( t.list, '([^,]*)($|,)', 1, l.lvl, NULL, 1 ) AS item, l.lvl FROM table_name t CROSS APPLY ( SELECT LEVEL AS lvl FROM DUAL CONNECT BY LEVEL <= REGEXP_COUNT( t.list, ',' ) + 1 ) l; Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 GoalKicker.com – Oracle® Database Notes for Professionals 56 Section 21.6: Splitting Strings using XMLTable and FLWOR expressions This solution uses the ora:tokenize XQuery function that is available from Oracle 11. Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list Query: SELECT t.id, x.item, x.lvl FROM table_name t, XMLTABLE( 'let $list := ora:tokenize(.,","), $cnt := count($list) for $val at $r in $list where $r < $cnt return $val' PASSING list||',' COLUMNS item VARCHAR2(100) PATH '.', lvl FOR ORDINALITY ) (+) x; Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) (NULL) 4 f 1 4 (NULL) 2 4 g 3 Section 21.7: Splitting Delimited Strings using XMLTable Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL FROM DUAL UNION ALL -- NULL list SELECT 4, 'f,,g' FROM DUAL; -- NULL item in the list GoalKicker.com – Oracle® Database Notes for Professionals 57 Query: SELECT t.id, SUBSTR( x.item.getStringVal(), 2 ) AS item, x.lvl FROM table_name t CROSS JOIN XMLTABLE( ( '"#' || REPLACE( t.list, ',', '","#' ) || '"' ) COLUMNS item XMLTYPE PATH '.', lvl FOR ORDINALITY ) x; (Note: the # character is appended to facilitate extracting NULL values; it is later removed using SUBSTR( item, 2 ). If NULL values are not required then you can simplify the query and omit this.) Output: ID ITEM LVL ---------- ------- ---------- 1 a 1 1 b 2 1 c 3 1 d 4 2 e 1 3 (NULL) 1 4 f 1 4 (NULL) 2 4 g 3 GoalKicker.com – Oracle® Database Notes for Professionals 58 Chapter 22: Collections and Records Section 22.1: Use a collection as a return type for a split function It's necessary to declare the type; here t_my_list; a collection is a TABLE OF something CREATE OR REPLACE TYPE t_my_list AS TABLE OF VARCHAR2(100); Here's the function. Notice the () used as a kind of constructor, and the COUNT and EXTEND keywords that help you create and grow your collection; CREATE OR REPLACE FUNCTION cto_table(p_sep IN VARCHAR2, p_list IN VARCHAR2) RETURN t_my_list AS --- this function takes a string list, element being separated by p_sep -- as separator l_string VARCHAR2(4000) := p_list || p_sep; l_sep_index PLS_INTEGER; l_index PLS_INTEGER := 1; l_tab t_my_list := t_my_list(); BEGIN LOOP l_sep_index := INSTR(l_string, p_sep, l_index); EXIT WHEN l_sep_index = 0; l_tab.EXTEND; l_tab(l_tab.COUNT) := TRIM(SUBSTR(l_string,l_index,l_sep_index - l_index)); l_index := l_sep_index + 1; END LOOP; RETURN l_tab; END cto_table; / Then you can see the content of the collection with the TABLE() function from SQL; it can be used as a list inside a SQL IN ( ..) statement: SELECT * FROM A_TABLE WHERE A_COLUMN IN ( TABLE(cto_table('|','a|b|c|d')) ) --- gives the records where A_COLUMN in ('a', 'b', 'c', 'd') -- GoalKicker.com – Oracle® Database Notes for Professionals 59 Chapter 23: Object Types Section 23.1: Accessing stored objects CREATE SEQUENCE test_seq START WITH 1001; CREATE TABLE test_tab ( test_id INTEGER, test_obj base_type, PRIMARY KEY (test_id) ); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, base_type(1,'BASE_TYPE')); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, base_type(2,'BASE_TYPE')); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, mid_type(3, 'MID_TYPE',SYSDATE - 1)); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, mid_type(4, 'MID_TYPE',SYSDATE + 1)); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, leaf_type(5, 'LEAF_TYPE',SYSDATE - 20,'Maple')); INSERT INTO test_tab (test_id, test_obj) VALUES (test_seq.NEXTVAL, leaf_type(6, 'LEAF_TYPE',SYSDATE + 20,'Oak')); Returns object reference: SELECT test_id ,test_obj FROM test_tab; Returns object reference, pushing all to subtype SELECT test_id ,TREAT(test_obj AS mid_type) AS obj FROM test_tab; Returns a string descriptor of each object, by type SELECT test_id ,TREAT(test_obj AS base_type).to_string() AS to_string -- Parenthesis are needed after the function name, or Oracle will look for an attribute of this name. FROM test_tab; Section 23.2: BASE_TYPE Type declaration: CREATE OR REPLACE TYPE base_type AS OBJECT ( base_id INTEGER, base_attr VARCHAR2(400), null_attr INTEGER, -- Present only to demonstrate non-default constructors CONSTRUCTOR FUNCTION base_type ( i_base_id INTEGER, GoalKicker.com – Oracle® Database Notes for Professionals 60 i_base_attr VARCHAR2 ) RETURN SELF AS RESULT, MEMBER FUNCTION get_base_id RETURN INTEGER, MEMBER FUNCTION get_base_attr RETURN VARCHAR2, MEMBER PROCEDURE set_base_id(i_base_id INTEGER), MEMBER PROCEDURE set_base_attr(i_base_attr VARCHAR2), MEMBER FUNCTION to_string RETURN VARCHAR2 ) INSTANTIABLE NOT FINAL Type body: CREATE OR REPLACE TYPE BODY base_type AS CONSTRUCTOR FUNCTION base_type ( i_base_id INTEGER, i_base_attr VARCHAR2 ) RETURN SELF AS RESULT IS BEGIN self.base_id := i_base_id; self.base_attr := i_base_attr; RETURN; END base_type; MEMBER FUNCTION get_base_id RETURN INTEGER IS BEGIN RETURN self.base_id; END get_base_id; MEMBER FUNCTION get_base_attr RETURN VARCHAR2 IS BEGIN RETURN self.base_attr; END get_base_attr; MEMBER PROCEDURE set_base_id(i_base_id INTEGER) IS BEGIN self.base_id := i_base_id; END set_base_id; MEMBER PROCEDURE set_base_attr(i_base_attr VARCHAR2) IS BEGIN self.base_attr := i_base_attr; END set_base_attr; MEMBER FUNCTION to_string RETURN VARCHAR2 IS BEGIN RETURN 'BASE_ID ['||self.base_id||']; BASE_ATTR ['||self.base_attr||']'; END to_string; END; Section 23.3: MID_TYPE Type declaration: CREATE OR REPLACE TYPE mid_type UNDER base_type ( mid_attr DATE, CONSTRUCTOR FUNCTION mid_type ( i_base_id INTEGER, GoalKicker.com – Oracle® Database Notes for Professionals 61 i_base_attr VARCHAR2, i_mid_attr DATE ) RETURN SELF AS RESULT, MEMBER FUNCTION get_mid_attr RETURN DATE, MEMBER PROCEDURE set_mid_attr(i_mid_attr DATE), OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2 ) INSTANTIABLE NOT FINAL Type body: CREATE OR REPLACE TYPE BODY mid_type AS CONSTRUCTOR FUNCTION mid_type ( i_base_id INTEGER, i_base_attr VARCHAR2, i_mid_attr DATE ) RETURN SELF AS RESULT IS BEGIN self.base_id := i_base_id; self.base_attr := i_base_attr; self.mid_attr := i_mid_attr; RETURN; END mid_type; MEMBER FUNCTION get_mid_attr RETURN DATE IS BEGIN RETURN self.mid_attr; END get_mid_attr; MEMBER PROCEDURE set_mid_attr(i_mid_attr DATE) IS BEGIN self.mid_attr := i_mid_attr; END set_mid_attr; OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2 IS BEGIN RETURN (SELF AS base_type).to_string || '; MID_ATTR [' || self.mid_attr || ']'; END to_string; END; Section 23.4: LEAF_TYPE Type declaration: CREATE OR REPLACE TYPE leaf_type UNDER mid_type ( leaf_attr VARCHAR2(1000), CONSTRUCTOR FUNCTION leaf_type ( i_base_id INTEGER, i_base_attr VARCHAR2, i_mid_attr DATE, i_leaf_attr VARCHAR2 ) RETURN SELF AS RESULT, MEMBER FUNCTION get_leaf_attr RETURN VARCHAR2, MEMBER PROCEDURE set_leaf_attr(i_leaf_attr VARCHAR2), OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2 ) INSTANTIABLE FINAL GoalKicker.com – Oracle® Database Notes for Professionals 62 Type Body: CREATE OR REPLACE TYPE BODY leaf_type AS CONSTRUCTOR FUNCTION leaf_type ( i_base_id INTEGER, i_base_attr VARCHAR2, i_mid_attr DATE, i_leaf_attr VARCHAR2 ) RETURN SELF AS RESULT IS BEGIN self.base_id := i_base_id; self.base_attr := i_base_attr; self.mid_attr := i_mid_attr; self.leaf_attr := i_leaf_attr; RETURN; END leaf_type; MEMBER FUNCTION get_leaf_attr RETURN VARCHAR2 IS BEGIN RETURN self.leaf_attr; END get_leaf_attr; MEMBER PROCEDURE set_leaf_attr(i_leaf_attr VARCHAR2) IS BEGIN self.leaf_attr := i_leaf_attr; END set_leaf_attr; OVERRIDING MEMBER FUNCTION to_string RETURN VARCHAR2 IS BEGIN RETURN (SELF AS mid_type).to_string || '; LEAF_ATTR [' || self.leaf_attr || ']'; END to_string; END; GoalKicker.com – Oracle® Database Notes for Professionals 63 Chapter 24: Loop Section 24.1: Simple Loop DECLARE v_counter NUMBER(2); BEGIN v_counter := 0; LOOP v_counter := v_counter + 1; DBMS_OUTPUT.put_line('Line number' || v_counter); EXIT WHEN v_counter = 10; END LOOP; END; Section 24.2: WHILE Loop The WHILE loop is executed untill the condition of end is fulfilled. Simple example: DECLARE v_counter NUMBER(2); --declaration of counter variable BEGIN v_counter := 0; --point of start, first value of our iteration WHILE v_counter < 10 LOOP --exit condition DBMS_OUTPUT.put_line('Current iteration of loop is ' || v_counter); --show current iteration number in dbms script output v_counter := v_counter + 1; --incrementation of counter value, very important step END LOOP; --end of loop declaration END; This loop will be executed untill current value of variable v_counter will be less than ten. The result: CURRENT iteration OF LOOP IS 0 CURRENT iteration OF LOOP IS 1 CURRENT iteration OF LOOP IS 2 CURRENT iteration OF LOOP IS 3 CURRENT iteration OF LOOP IS 4 CURRENT iteration OF LOOP IS 5 CURRENT iteration OF LOOP IS 6 CURRENT iteration OF LOOP IS 7 CURRENT iteration OF LOOP IS 8 CURRENT iteration OF LOOP IS 9 The most important thing is, that our loop starts with '0' value, so first line of results is 'Current iteration of loop is 0'. Section 24.3: FOR Loop Loop FOR works on similar rules as other loops. FOR loop is executed exact number of times and this number is GoalKicker.com – Oracle® Database Notes for Professionals 64 known at the beginning - lower and upper limits are directly set in code. In every step in this example, loop is increment by 1. Simple example: DECLARE v_counter NUMBER(2); --declaration of counter variable BEGIN v_counter := 0; --point of start, first value of our iteration, execute of variable FOR v_counter IN 1..10 LOOP --The point, where lower and upper point of loop statement is declared - in this example, loop will be executed 10 times, start with value of 1 DBMS_OUTPUT.put_line('Current iteration of loop is ' || v_counter); --show current iteration number in dbms script output END LOOP; --end of loop declaration END; And the result is: CURRENT iteration OF LOOP IS 1 CURRENT iteration OF LOOP IS 2 CURRENT iteration OF LOOP IS 3 CURRENT iteration OF LOOP IS 4 CURRENT iteration OF LOOP IS 5 CURRENT iteration OF LOOP IS 6 CURRENT iteration OF LOOP IS 7 CURRENT iteration OF LOOP IS 8 CURRENT iteration OF LOOP IS 9 CURRENT iteration OF LOOP IS 10 Loop FOR has additional property, which is working in reverse. Using additional word 'REVERSE' in declaration of lower and upper limit of loop allow to do that. Every execution of loop decrement value of v_counter by 1. Example: DECLARE v_counter NUMBER(2); --declaration of counter variable BEGIN v_counter := 0; --point of start FOR v_counter IN REVERSE 1..10 LOOP DBMS_OUTPUT.put_line('Current iteration of loop is ' || v_counter); --show current iteration number in dbms script output END LOOP; --end of loop declaration END; And the result: CURRENT iteration OF LOOP IS 10 CURRENT iteration OF LOOP IS 9 CURRENT iteration OF LOOP IS 8 CURRENT iteration OF LOOP IS 7 CURRENT iteration OF LOOP IS 6 GoalKicker.com – Oracle® Database Notes for Professionals 65 CURRENT iteration OF LOOP IS 5 CURRENT iteration OF LOOP IS 4 CURRENT iteration OF LOOP IS 3 CURRENT iteration OF LOOP IS 2 CURRENT iteration OF LOOP IS 1 GoalKicker.com – Oracle® Database Notes for Professionals 66 Chapter 25: Cursors Section 25.1: Parameterized "FOR loop" Cursor DECLARE CURSOR c_emp_to_be_raised(p_sal emp.sal%TYPE) IS SELECT * FROM emp WHERE sal < p_sal; BEGIN FOR cRowEmp IN c_emp_to_be_raised(1000) LOOP DBMS_OUTPUT.Put_Line(cRowEmp .eName ||' ' ||cRowEmp.sal||'... should be raised ;)'); END LOOP; END; / Section 25.2: Implicit "FOR loop" cursor BEGIN FOR x IN (SELECT * FROM emp WHERE sal < 100) LOOP DBMS_OUTPUT.Put_Line(x.eName ||' '||x.sal||'... should REALLY be raised :D'); END LOOP; END; / First advantage is there is no tedious declaration to do (think of this horrible "CURSOR" thing you had in previous versions) second advantage is you first build your select query, then when you have what you want, you immediately can access the fields of your query (x.) in your PL/SQL loop The loop opens the cursor and fetches one record at a time for every loop. At the end of the loop the cursor is closed. Implicit cursors are faster because the interpreter's work grows as the code gets longer. The less code the less work the interpreter has to do. Section 25.3: Handling a CURSOR Declare the cursor to scan a list of records Open it Fetch current record into variables (this increments position) Use %notfound to detect end of list Don't forget to close the cursor to limit resources consumption in current context -- DECLARE CURSOR curCols IS -- select column name and type from a given table SELECT column_name, data_type FROM all_tab_columns WHERE table_name='MY_TABLE'; v_tab_column all_tab_columns.column_name%TYPE; v_data_type all_tab_columns.data_type%TYPE; v_ INTEGER := 1; BEGIN OPEN curCols; LOOP FETCH curCols INTO v_tab_column, v_data_type; IF curCols%notfound OR v_ > 2000 THEN EXIT; END IF; GoalKicker.com – Oracle® Database Notes for Professionals 67 DBMS_OUTPUT.put_line(v_||':Column '||v_tab_column||' is of '|| v_data_type||' Type.'); v_:= v_ + 1; END LOOP; -- Close in any case IF curCols%ISOPEN THEN CLOSE curCols; END IF; END; / Section 25.4: Working with SYS_REFCURSOR SYS_REFCURSOR can be used as a return type when you need to easily handle a list returned not from a table, but more specifically from a function: function returning a cursor CREATE OR REPLACE FUNCTION list_of (required_type_in IN VARCHAR2) RETURN SYS_REFCURSOR IS v_ SYS_REFCURSOR; BEGIN CASE required_type_in WHEN 'CATS' THEN OPEN v_ FOR SELECT nickname FROM ( SELECT 'minou' nickname FROM dual UNION ALL SELECT 'minâ' FROM dual UNION ALL SELECT 'minon' FROM dual ); WHEN 'DOGS' THEN OPEN v_ FOR SELECT dog_call FROM ( SELECT 'bill' dog_call FROM dual UNION ALL SELECT 'nestor' FROM dual UNION ALL SELECT 'raoul' FROM dual ); END CASE; -- Whit this use, you must not close the cursor. RETURN v_; END list_of; / and how to use it: DECLARE v_names SYS_REFCURSOR; v_ VARCHAR2 (32767); BEGIN v_names := list_of('CATS'); LOOP FETCH v_names INTO v_; EXIT WHEN v_names%NOTFOUND; DBMS_OUTPUT.put_line(v_); END LOOP; -- here you close it CLOSE v_names; END; / GoalKicker.com – Oracle® Database Notes for Professionals 68 Chapter 26: Sequences Parameter Details schema schema name increment by interval between the numbers start with first number needed maxvalue Maximum value for the sequence nomaxvalue Maximum value is defaulted minvalue minimum value for the sequence nominvalue minimum value is defaulted cycle Reset to the start after reaching this value nocycle Default cache Preallocation limit nocache Default order Guarantee the order of numbers noorder default Section 26.1: Creating a Sequence: Example Purpose Use the CREATE SEQUENCE statement to create a sequence, which is a database object from which multiple users may generate unique integers. You can use sequences to automatically generate primary key values. When a sequence number is generated, the sequence is incremented, independent of the transaction committing or rolling back. If two users concurrently increment the same sequence, then the sequence numbers each user acquires may have gaps, because sequence numbers are being generated by the other user. One user can never acquire the sequence number generated by another user. After a sequence value is generated by one user, that user can continue to access that value regardless of whether the sequence is incremented by another user. Sequence numbers are generated independently of tables, so the same sequence can be used for one or for multiple tables. It is possible that individual sequence numbers will appear to be skipped, because they were generated and used in a transaction that ultimately rolled back. Additionally, a single user may not realize that other users are drawing from the same sequence. After a sequence is created, you can access its values in SQL statements with the CURRVAL pseudocolumn, which returns the current value of the sequence, or the NEXTVAL pseudocolumn, which increments the sequence and returns the new value. Prerequisites To create a sequence in your own schema, you must have the CREATE SEQUENCE system privilege. To create a sequence in another user's schema, you must have the CREATE ANY SEQUENCE system privilege. Creating a Sequence: Example The following statement creates the sequence customers_seq in the sample schema oe. This sequence could be used to provide customer ID numbers when rows are added to the customers table. CREATE SEQUENCE customers_seq START WITH 1000 INCREMENT BY 1 NOCACHE GoalKicker.com – Oracle® Database Notes for Professionals 69 NOCYCLE; The first reference to customers_seq.nextval returns 1000. The second returns 1001. Each subsequent reference will return a value 1 greater than the previous reference. GoalKicker.com – Oracle® Database Notes for Professionals 70 Chapter 27: Indexes Here I will explain different index using example, how index increase query performance, how index decrease DML performance etc Section 27.1: b-tree index CREATE INDEX ord_customer_ix ON orders (customer_id); By default, if we do not mention anything, oracle creates an index as a b-tree index. But we should know when to use it. B-tree index stores data as binary tree format. As we know that, index is a schema object which stores some sort of entry for each value for the indexed column. So, whenever any search happens on those columns, it checks in the index for the exact location of that record to access fast. Few points about indexing: To search for entry in the index, some sort of binary search algorithm used. When data cardinality is high, b-tree index is perfect to use. Index makes DML slow, as for each record, there should be one entry in the index for indexed column. So, if not necessary, we should avoid creating index. Section 27.2: Bitmap Index CREATE BITMAP INDEX emp_bitmap_idx ON index_demo (gender); Bitmap index is used when data cardinality is low. Here, Gender has value with low cardinality. Values are may be Male, Female & others. So, if we create a binary tree for this 3 values while searching it will have unnecessary traverse. In bitmap structures, a two-dimensional array is created with one column for every row in the table being indexed. Each column represents a distinct value within the bitmapped index. This two-dimensional array represents each value within the index multiplied by the number of rows in the table. At row retrieval time, Oracle decompresses the bitmap into the RAM data buffers so it can be rapidly scanned for matching values. These matching values are delivered to Oracle in the form of a Row-ID list, and these Row-ID values may directly access the required information. Section 27.3: Function Based Index CREATE INDEX first_name_idx ON user_data (UPPER(first_name)); SELECT * FROM user_data WHERE UPPER(first_name) = 'JOHN2'; Function based index means, creating index based on a function. If in search (where clause), frequently any function is used, it's better to create index based on that function. Here, in the example, for search, Upper() function is being used. So, it's better to create index using upper function. GoalKicker.com – Oracle® Database Notes for Professionals 71 Chapter 28: Hints Parameters Details Degree of Parallelism (DOP) It is the number of parallel connection/processes which you want your query to open up. It is usually 2, 4, 8, 16 so on. Table Name The name of the table on which parallel hint will be applied. Section 28.1: USE_NL Use Nested Loops. Usage : use_nl(A B) This hint will ask the engine to use nested loop method to join the tables A and B. That is row by row comparison. The hint does not force the order of the join, just asks for NL. SELECT /*+use_nl(e d)*/ * FROM Employees E JOIN Departments D ON E.DepartmentID = D.ID Section 28.2: APPEND HINT "Use DIRECT PATH method for inserting new rows". The APPEND hint instructs the engine to use direct path load. This means that the engine will not use a conventional insert using memory structures and standard locks, but will write directly to the tablespace the data. Always creates new blocks which are appended to the table's segment. This will be faster, but have some limitations: You cannot read from the table you appended in the same session until you commmit or rollback the transaction. If there are triggers defined on the table Oracle will not use direct path(it's a different story for sqlldr loads). others Example. INSERT /*+append*/ INTO Employees SELECT * FROM Employees; Section 28.3: Parallel Hint Statement-level parallel hints are the easiest: SELECT /*+ PARALLEL(8) */ first_name, last_name FROM employee emp; Object-level parallel hints give more control but are more prone to errors; developers often forget to use the alias instead of the object name, or they forget to include some objects. SELECT /*+ PARALLEL(emp,8) */ first_name, last_name FROM employee emp; SELECT /*+ PARALLEL(table_alias,Degree of Parallelism) */ FROM table_name table_alias; Let's say a query takes 100 seconds to execute without using parallel hint. If we change DOP to 2 for same query, GoalKicker.com – Oracle® Database Notes for Professionals 72 then ideally the same query with parallel hint will take 50 second. Similarly using DOP as 4 will take 25 seconds. In practice, parallel execution depends on many other factors and does not scale linearly. This is especially true for small run times where the parallel overhead may be larger than the gains from running in multiple parallel servers. Section 28.4: USE_HASH Instructs the engine to use hash method to join tables in the argument. Usage : use_hash(TableA [TableB] ... [TableN]) As explained in many places, "in a HASH join, Oracle accesses one table (usually the smaller of the joined results) and builds a hash table on the join key in memory. It then scans the other table in the join (usually the larger one) and probes the hash table for matches to it." It is preferred against Nested Loops method when the tables are big, no indexes are at hand, etc. Note: The hint does not force the order of the join, just asks for HASH JOIN method. Example of usage: SELECT /*+use_hash(e d)*/ * FROM Employees E JOIN Departments D ON E.DepartmentID = D.ID Section 28.5: FULL The FULL hint tells Oracle to perform a full table scan on a specified table, no matter if an index can be used. CREATE TABLE fullTable(id) AS SELECT LEVEL FROM dual CONNECT BY LEVEL < 100000; CREATE INDEX idx ON fullTable(id); With no hints, the index is used: SELECT COUNT(1) FROM fullTable f WHERE id BETWEEN 10 AND 100; -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 13 | 3 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 13 | | | |* 2 | INDEX RANGE SCAN| IDX | 2 | 26 | 3 (0)| 00:00:01 | -------------------------------------------------------------------------- FULL hint forces a full scan: SELECT /*+ full(f) */ COUNT(1) FROM fullTable f WHERE id BETWEEN 10 AND 100; -------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 13 | 47 (3)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | 13 | | | |* 2 | TABLE ACCESS FULL| FULLTABLE | 2 | 26 | 47 (3)| 00:00:01 | -------------------------------------------------------------------------------- GoalKicker.com – Oracle® Database Notes for Professionals 73 Section 28.6: Result Cache Oracle (11g and above) allows the SQL queries to be cached in the SGA and reused to improve performance. It queries the data from cache rather than database. Subsequent execution of same query is faster because now the data is being pulled from cache. SELECT /*+ result_cache */ NUMBER FROM main_table; Output - Number ------ 1 2 3 4 5 6 7 8 9 10 Elapsed: 00:00:02.20 If I run the same query again now, the time to execute will reduce since the data is now fetched from cache which was set during the first execution. Output - Number ------ 1 2 3 4 5 6 7 8 9 10 Elapsed: 00:00:00.10 Notice how the elapsed time reduced from 2.20 seconds to 0.10 seconds. Result Cache holds the cache until the data in database is updated/altered/deleted. Any change will release the cache. GoalKicker.com – Oracle® Database Notes for Professionals 74 """